Researchers are hoping to improve
high-precision clocks by entangling their atoms.
by Patrick L Barry and Dr Tony
Einstein called it
"spooky action at a distance." Now researchers are using an astonishing
property of quantum mechanics called "entanglement" to improve atomic
clocks - humanity's most precise way to measure time. Entangled
clocks could be as much as 1000 times more stable than their non-entangled
This improvement would
benefit pilots, farmers, hikers - in short, anyone who uses the Global
Positioning System (GPS). Each of the 24+ GPS satellites carries
four atomic clocks on board. By triangulating time signals broadcast
from orbit, GPS receivers on the ground can pinpoint their own location
NASA uses atomic clocks
for spacecraft navigation. Geologists use them to monitor continental
drift and the slowly changing spin of our planet. Physicists use
them to check theories of gravity. An entangled atomic clock might
keep time precisely enough to test the value of the Fine Structure
Constant, one of the fundamental constants of physics.
"The ability to measure
time with very high precision is an invaluable tool for scientific
research and for technology," says Alex Kuzmich, a physicist at
the Georgia Institute of Technology.
Through its office
of Biological and Physical Research, NASA recently awarded a grant
to Kuzmich and his colleagues to support their research. Kuzmich
has studied quantum entanglement for the last 10 years and has recently
turned to exploring how it can be applied to atomic clocks.
Einstein never liked
entanglement. It seemed to run counter to a central tenet of his
theory of relativity: nothing, not even information, can travel
faster than the speed of light. In quantum mechanics, all the forces
of nature are mediated by the exchange of particles such as photons,
and these particles must obey this cosmic speed limit. So an action
"here" can cause no effect "over there" any sooner than it would
take light to travel there in a vacuum.
Image by Patrick L. Barry
a measurement on one entangled particle affects the properties
of the other instantaneously.
But two entangled particles
can appear to influence one another instantaneously, whether they're
in the same room or at opposite ends of the Universe. Pretty spooky
occurs when two or more particles interact in a way that causes
their fates to become linked: It becomes impossible to consider
(or mathematically describe) each particle's condition independently
of the others'. Collectively they constitute a single quantum state.
Two entangled particles
often must have opposite values for a property - for example, if
one is spinning in "up" direction, the other must be spinning in
the "down" direction. Suppose you measure one of the entangled particles
and, by doing so, you nudge it "up." This causes the entangled partner
to spin "down." Making the measurement "here" affected the other
particle "over there" instantaneously, even if the other particle
was a million miles away.
While physicists and philosophers grapple with the implications
for the nature of causation and the structure of the Universe, some
physicists are busy putting entanglement to work in applications
such as "teleporting" atoms and producing uncrackable encryption.
Atomic clocks also
stand to benefit. "Entangling the atoms in an atomic clock reduces
the inherent uncertainties in the system," Kuzmich explains.
At the heart of every
atomic clock lies a cloud of atoms, usually cesium or rubidium.
The natural resonance's of these atoms serve the same purpose as
the pendulum in a grandfather clock. Tick-tock-tick-tock. A laser
beam piercing the cloud can count the oscillations and use them
to keep time. This is how an atomic clock works.
"The best atomic clocks
on Earth today are stable to about one part in 1015,"
notes Kuzmich. That means an observer would have to watch the clock
for 1015 seconds or 30 million years to see it gain or
lose a single second.
Click on the image to learn more.
Lasers are a key ingredient of atomic clocks - both the ordinary and
The precision of an
atomic clock depends on a few things, including the number of atoms
being used. The more atoms, the better. In a normal atomic clock,
the precision is proportional to the square-root of the number of
atoms. So having, say, 4 times as many atoms would only double the
precision. In an entangled atomic clock, however, the improvement
is directly proportional to the number of atoms. Four times more
atoms makes a 4-times better clock.
Using plenty of atoms,
it might be possible to build a "maximally entangled clock stable
to about one part in 1018," says Kuzmich. You would have
to watch that clock for 1018 seconds or 30 billion years
to catch it losing a single second.
Kuzmich plans to use
the lasers already built-in to atomic clocks to create the entanglement.
"We will measure the
phase of the laser light passing through the cloud of atoms," he
explains. Measuring the phase "tweaks the laser beam," and if the
frequency of the laser has been chosen properly, tweaking the beam
causes the atoms to become entangled. Or, as one quantum physicist
might say to another, "such a procedure amounts to a quantum non-demolition
(QND) measurement on the atoms, and results in preparation of a
Squeezed Spin State."
How soon an entangled
clock could be built - much less launched into space aboard a hypothetical
new generation of GPS satellites - is difficult to predict, cautions
Kuzmich. The research is still at the stage of just demonstrating
the principle. Building a working prototype is probably several
But thanks to research such as this, having still-better atomic
clocks available to benefit science and technology is only a matter


Wonders of Bird Migration - and Threatened Asian Wetlands
Birds may undertake marathon flights using astonishing navigation skills – yet are threatened by careless habitat destruction
As you read this, flocks of bar-tailed godwits may be departing the south coast of Alaska. These brown wading birds appear fairly nondescript – like smaller cousins of curlew – but are embarking on one of the greatest migratory journeys known.
The godwits are will fly non-stop for some 11,700 km (7270 miles), the distance from Hong Kong to Los Angeles, and the longest known flight by any creature. After perhaps eight days, they will arrive at their destination, coastal mudflats in New Zealand. Church bells will ring to welcome flocks touching down in Christchurch, where they are regarded as harbingers of spring.
Bird migration is among the wonders of the natural world. It has evolved in response to the great rewards of being able to exploit food in a place like Arctic tundra, whilst also fleeing winter conditions that make life impossible for a many birds. Yet there are also immense risks, and countless birds die en route.
Amazing adaptations of migratory birds
Migratory birds have a host of remarkable adaptations that enable them to undertake such journeys. To prepare for their autumn marathon, the bar-tailed godwits store energy, until fat comprises up to 55 percent of their body weight. Their livers, kidneys and intestines shrink, becoming almost useless, as the birds’ bodies become focused on flying.
The godwits have innate weather forecasting skills: “All the departures we’ve observed to date were associated with low pressure systems,” noted Bob Gill, a wildlife biologist with the US Geological Survey’s Alaska Science Center, who was in a team studying godwits. “The birds get on the back side of these lows and get 900 to 1,200 kilometres (558 to 744 miles) of pretty strong tailwinds.”
Built-in weather knowledge could also help the godwits avoid being buffeted by Pacific typhoons. No one knows for sure, just as no one fully understands how birds navigate.
Navigation may involve quantum mechanics!
Experiments have revealed that birds can use a range of methods to help with navigation. The most obvious of these is following familiar landmarks, such as rivers, coastlines and even highways that feature in their mental maps. At least some migrants have mental star maps, for orientation on clear nights, and indicating arrival at their destinations.
The height and position of the sun can help birds judge the direction in which they’re headed. Yet this is no help in cloudy weather, nor can just observing the sun fix position when there are no landmarks in view – which proved so challenging for humans that it was not until the late 18th century that mariners could determine longitude while at sea. For precisely determining their position and direction, birds need a sense we don’t consciously possess: gauging the earth’s magnetic field.
Experiments have shown that birds can orient using magnetic fields, and a change as small as a thousandth of the earth’s magnetic field can affect the navigation ability of European robins. Yet it is unclear how they sense magnetism. There were notions that iron-rich cells near pigeons’ beaks serve as tiny compasses. But researchers have found only white blood cells that do not produce electrical signals. The true answer could be far more bizarre.
Robins’ magnetic sense requires them to see clearly – in turn leading to notions that it depends on a weird property of matter known as quantum entanglement. Possibly, light excites two electrons on a molecule of a suitable chemical, leading to one electron departing for another molecule of the same chemical. Though the electrons are now separate, their “spins” would be inextricably linked for a short time, during which they would be affected by the earth’s magnetic field. The magnetism could affect the chemical’s properties, resulting in subtle changes across the eye that lead to a bird “seeing” the earth’s magnetic field.
A candidate for the chemical responsible for sensing magnetism is a protein known as cryptochrome. Intriguingly, fruit flies with cryptochrome receptors can navigate using magnetism; those without fly as if oblivious to the magnetic field.
Bar-tailed Godwit: the marathon bird
While the ways birds navigate remain mysterious, we have far more knowledge of the routes they take. This is partly thanks to satellite tracking of birds including the bar-tailed godwit given the code E7.
E7 is a female bar-tailed godwit that was captured, tagged and fitted with a satellite transmitter in New Zealand in February 2007. No one was then certain that these godwits really flew the length of the Pacific in one flight, yet in autumn that year scientists monitored as she left Alaska on 29 August, passed near Fiji, and on 7 September landed at an estuary eight miles from where she had been captured. In March, E7 had made two other huge flights: taking her to coastal mudflats in north China, 10,300km (6400 miles) away, and then another 6500km (4500 miles) to Alaska.
Threatened Yellow Sea wetlands
While in north China, E7 spent five weeks refuelling in readiness for the breeding season ahead. Tens of thousands of other godwits were likewise refuelling at this and other wetlands around the Yellow Sea – which is among the world’s greatest areas for intertidal mudflats and the wildlife that depends on them. According to WWF China, the Yellow Sea is the most important site for migratory birds in the East Asian-Australasian Flyway, which encompasses the routes of a myriad species. Millions of birds pass through each year.
Red Knot and Great Knot at Happy Island, southeast of Tianjin
The godwits are among an outstanding variety of shorebirds that rely on the Yellow Sea wetlands as stopovers on their journeys. There are also geese, ducks, cranes, cormorants and other wetland birds. Some species are unique to east Asia, some face extinction; one, spoon-billed sandpiper, probably numbers less than 500 in all.
Yet while the Yellow Sea should be a key region for conservation efforts, wetlands are being casually destroyed. Within the last decade, South Korea reclaimed an estuary eight times larger than Hong Kong Island. There are ongoing massive reclamation projects along the Chinese shore – notably in Tianjin which, ironically, is also building an artificial “eco city”. Water pollution is severe.
Wetlands are also threatened elsewhere along the flyway, including in Hong Kong. As habitats dwindle, populations of the migratory birds depending on them will continue to decline. Year by year, there will be less wonder in the world. Perhaps a season will come when the church bells in Christchurch remain silent, as godwit flocks no longer arrive.
Published in Sunday Morning Post, Hong Kong, on 2 September 2012.
Useful links include:
Bar-tailed Godwit (Limosa lapponica) on US Geological Survey website; includes the astonishing flights of godwit E7.
On this site, there's Reclamations slaughtering Bohai Bay birds.


Bohr and beyond: a century of quantum physics
Our understanding of the quantum world began with Niels Bohr's discovery of the quantum atom in 1913. Bohr would be astounded by where his theory has since led, says Professor David Jamieson.
Bohr's discovery of the quantum nature of the atom, published when he was a young man of 28, was an important pioneering contribution to the earliest days of quantum physics.
This field emerged to explain the common sense-defying behaviour of atoms, molecules and light at the smallest scales, forming the foundations on which we have built one of the greatest and most successful theories of all time — quantum mechanics.
What is quite remarkable to modern eyes was that Bohr had very little to go on.
The true nature of the atom as an incredibly tiny nucleus surrounded by a cloud of orbiting electrons had only been discovered a few years earlier, in the separate work of physicists Thomson and Rutherford.
Bohr's genius was to recognise that these electrons had many roles in a range of apparently different scenarios. He saw that electrons were behind the electric currents flowing in wires, the red hot glow of molten iron, and the production of light from electric discharges in gas-filled tubes.
Bohr took the important elements of the emerging theories to explain all these different things, invented some new quantum mechanical principles and made it all work.
In so doing he also managed to solve an important and troubling problem: that any electron moving in an orbit would have to spontaneously radiate away energy until it spiralled down and slowed to a stop — a view from classical physics that meant no atom could be stable.
Bohr's quantum atom: nature is digital
Like others, Bohr was keen to draw on our understanding of the orbit of planets around the sun in understanding the orbit of electrons in atoms.
The planets are attracted by the powerful gravity of the sun, but their speed lets them settle into stable orbits rather than spiralling into the sun's gravitational field.
In the case of the positively charged nucleus and the negatively charged electron, the mutual pull is the electric force. Classical physics dictates that an accelerating charge (like an electron in orbit) must give off electromagnetic radiation. The energy lost through radiation should make an electron slow in its orbit and quickly crash into the nucleus, which means no atom could be stable. This was clearly not true, and Bohr's solution to this conundrum was the first of two powerful ideas with which he introduced us to the quantum atom.
He proposed that electrons in atoms are only stable in certain allowed orbits, which he called stationary states. This idea is an attribute of the wave-like nature of all matter at the nanoscale, and it is now understood as a fundamental principle of quantum mechanics.
Bohr's second idea was that electrons dropping down from one stable orbit to another would radiate a single discrete packet of radiation, in the form of a photon of light. This shows the deep connection between light and matter, and that photons are all or nothing — there is no such thing as half a photon. Together these ideas tell us that nature is fundamentally digital at the atomic level, and they provide the basis for quantum mechanics.
From theory to evidence
Bohr was able to use his new theory to successfully explain the regularities in the pattern of light emitted from hot hydrogen gas, both in the laboratory and in the atmospheres of stars near and far. Heated hydrogen emits characteristic blue, red and violet light. Bohr showed that the light was given off by excited electrons as they settle into allowed stable orbits at lower energies. A photon of each of those colours of light corresponds to the energy difference between different allowed orbits.
The radiation emerging from the atom as the electrons settle into stable orbits can tell us a lot about the nucleus. Shortly after Bohr's discovery, Henry Moseley discovered that energetic photons emitted from electrons settling into close orbits around the nucleus, typically in the x-ray part of the spectrum, could be used to discover gaps in the periodic table of the elements where new elements would later be found. Later, Bohr's theory was further developed to explain molecules and the basis of chemistry.
One year after Bohr's theory appeared in the scientific journals, the British Association for the Advancement of Science held its 1914 meeting in Australia. In the old physics building at the University of Melbourne, Sir Ernest Rutherford presented a report on the new and controversial theory to delegates from the United Kingdom, Australia and New Zealand.
This was one of the first public outings for the theory. Reports from the conference give a strong sense of the excitement created by Bohr's radical ideas — one delegate remarked "... I should like to say that although I have criticised certain parts of Bohr's theory adversely, no one can admire more its ingenuity and great suggestiveness." These were prophetic words!
Today, Bohr's theory is applied to a range of scenarios that would have astounded the young Niels.
He could never have imagined that his work would lead to PET (positron emission tomography) scanners that look inside our bodies, showing us the effect of diseases like cancer on the way our organs function. Bohr's theory explains the mutual orbit of electrons and positrons just before they annihilate each other, transforming into gamma rays that give rise to the PET scan image.
And recent breakthroughs have led to some exciting new applications built on Bohr's theory, including our work in nanodiamonds and quantum computing at the Australian Centre of Excellence for Quantum Computation and Communication Technology.
Bohr in today's science: nanodiamonds, quantum computers ...
Bohr's theory can be adapted to explain the peculiar orbits of electrons around a single nitrogen atom inserted into a diamond crystal. The light photons emitted when these electrons change between their stationary states is incredibly bright, and signals the internal quantum state even at room temperature. These stationary states are susceptible to even the tiniest magnetic fields, affecting the colour of light given off. When a living cell is seeded with nanoscale diamond crystals containing single nitrogen atoms, the way the cellular electromagnetic machinery affects the emitted light tells us what is going on at these tiny scales. This could help us learn about the dynamics of biological neural networks, which is fundamental to gaining insight into information processing in the brain.
We have also shown how modern nanotechnology allows us to program digital information into the quantum atom. Recognising that both the electrons and the nucleus in the quantum atom possess angular momentum, called spin, we have discovered how to amplify one billion-fold the subtle difference in energy between the two stable spin states of the nucleus of an engineered phosphorus atom in a silicon device. This could lead to a raft of new technologies built on the quantum atom.
For example, instead of seeking information from the photons emerging from quantum atoms, we use photons in our single atom device as a means of artificially encoding information in the nuclear spin orientation. This could be the foundational component of a large-scale silicon quantum computer. In this device the electron spin is used for information processing and read-out, with the nuclear spin used as long lived memory for quantum information.
A quantum computer could have revolutionary applications to the storage, processing and transmission of information. This would exploit the best characteristics of the quantum domain and the most important material for microelectronics, silicon, to build the proposed quantum internet of the mid-21st century.
... and the Higgs boson
After Bohr published his ideas in 1913 he went on to found an important institute for theoretical physics in Copenhagen, and his great discovery was recognised by a Nobel Prize in 1922. He pledged support for founding the CERN laboratory in 1952 and then hosted the CERN theorists in his institute until they were ready to move to Geneva. Australian involvement in CERN led to the announcement in 2012 in Melbourne and Geneva of the discovery of the Higgs boson, the latest discovery in the deep journey into the quantum atom that Bohr helped start one hundred years ago!
About the author:Prof David Jamieson is Head of the School of Physics of the University of Melbourne, and a Program Manager with the Centre of Excellence for Quantum Computation and Communication Technology. His research expertise is in the field of ion beam physics, particularly in the use of focused ion beams for materials modification and analysis.
Published 18 July 2013


Scientists demonstrate versatile, noise-tolerant quantum operations on a single electron
While a classical bit found in conventional electronics exists only in binary 1 or 0 states, the more resourceful quantum bit, or 'qubit' is represented by a vector, pointing to a simultaneous combination of the 1 and 0 states. To fully implement a qubit, it is necessary to control the direction of this qubit's vector, which is generally done using fine-tuned and noise-isolated procedures.
Researchers at the University of Chicago's Institute for Molecular Engineering and the University of Konstanz have demonstrated the ability to generate a quantum logic operation, or rotation of the qubit, that - surprisingly -- is intrinsically resilient to noise as well as to variations in the strength or duration of the control. Their achievement is based on a geometric concept known as the Berry phase and is implemented through entirely optical means within a single electronic spin in diamond.
Their findings were published online Feb. 15, 2016, in Nature Photonics and will appear in the March print issue. "We tend to view quantum operations as very fragile and susceptible to noise, especially when compared to conventional electronics," remarked David Awschalom, the Liew Family Professor of Molecular Engineering and senior scientist at Argonne National Laboratory, who led the research. "In contrast, our approach shows incredible resilience to external influences and fulfills a key requirement for any practical quantum technology."
When a quantum mechanical object, such as an electron, is cycled along some loop, it retains a memory of the path that it travelled, the Berry phase. To better understand this concept, the Foucault pendulum, a common staple of science museums helps to give some intuition. A pendulum, like those in a grandfather clock, typically oscillates back and forth within a fixed plane. However, a Foucault pendulum oscillates along a plane that gradually rotates over the course of a day due to Earth's rotation, and in turn knocks over a series of pins encircling the pendulum.
The number of knocked-over pins is a direct measure of the total angular shift of the pendulum's oscillation plane, its acquired geometric phase. Essentially, this shift is directly related to the location of the pendulum on Earth's surface as the rotation of Earth transports the pendulum along a specific closed path, its circle of latitude. While this angular shift depends on the particular path traveled, Awschalom said, it remarkably does not depend on the rotational speed of Earth or the oscillation frequency of the pendulum.
"Likewise, the Berry phase is a similar path-dependent rotation of the internal state of a quantum system, and it shows promise in quantum information processing as a robust means to manipulate qubit states," he said.
A light touch
In this experiment, the researchers manipulated the Berry phase of a quantum state within a nitrogen-vacancy (NV) center, an atomic-scale defect in diamond. Over the past decade and a half, its electronic spin state has garnered great interest as a potential qubit. In their experiments, the team members developed a method with which to draw paths for this defect's spin by varying the applied laser light. To demonstrate Berry phase, they traced loops similar to that of a tangerine slice within the quantum space of all of the potential combinations of spin states.
"Essentially, the area of the tangerine slice's peel that we drew dictated the amount of Berry phase that we were able to accumulate," said Christopher Yale, a postdoctoral scholar in Awschalom's laboratory, and one of the co-lead authors of the project.
This approach using laser light to fully control the path of the electronic spin is in contrast to more common techniques that control the NV center spin, through the application of microwave fields. Such an approach may one day be useful in developing photonic networks of these defects, linked and controlled entirely by light, as a way to both process and transmit quantum information.
A noisy path
A key feature of Berry phase that makes it a robust quantum logic operation is its resilience to noise sources. To test the robustness of their Berry phase operations, the researchers intentionally added noise to the laser light controlling the path. As a result, the spin state would travel along its intended path in an erratic fashion. However, as long as the total area of the path remained the same, so did the Berry phase that they measured.
"In particular, we found the Berry phase to be insensitive to fluctuations in the intensity of the laser. Noise like this is normally a bane for quantum control," said Brian Zhou, a postdoctoral scholar in the group, and co-lead author.
"Imagine you're hiking along the shore of a lake, and even though you continually leave the path to go take pictures, you eventually finish hiking around the lake," said F. Joseph Heremans, co-lead author, and now a staff scientist at Argonne National Laboratory. "You've still hiked the entire loop regardless of the bizarre path you took, and so the area enclosed remains virtually the same."
These optically controlled Berry phases within diamond suggest a route toward robust and fault-tolerant quantum information processing, noted Guido Burkard, professor of physics at the University of Konstanz and theory collaborator on the project.
"Though its technological applications are still nascent, Berry phases have a rich underlying mathematical framework that makes them a fascinating area of study," Burkard said.
Steve Koppes | EurekAlert!
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The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
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Previous section: Encryption standards and Bullrun
In the foreseeable future, some standard encryption methods could become obsolete thanks to a brand-new technology. Quantum computing takes place on the atomic and sub-atomic scale and is still at the experimental stage. It aims to take advantage of some frankly mind-blowing properties of the particles that form the building blocks of matter and light and works in a completely different way from the classical electronics-based computing with which we are all familiar.
A bit in a classical computer is set to either 0 or 1 at any given moment in time. A classical computer program might be written to add two whole numbers, each of which has to be between zero and fifteen. Storing a number between zero and fifteen requires four bits (two to the power of four is sixteen), so storing both numbers would require eight bits. The values of each of the eight bits at the point in time when the program carried out the addition would determine the result.
Contrary to everything common sense tells us, a bit in a quantum computer, which is called a qubit, can have both values – 0 and 1 – simultaneously. A quantum program might take eight qubits as its input. Because each qubit has two values at once, eight qubits together have 256 concurrent values (two to the power of eight). The quantum program would effectively perform 256 calculations at the same time.
Unfortunately, the fact that each qubit in a quantum computation has both possible values at once does not mean that the results of a huge number of mathematical calculations can all be obtained using a single quantum computation. Rather than saying that each qubit has both values, it would perhaps be more accurate to say that each qubit has either value with a given probability. As long as a computation is taking place, each qubit really is set to 0 and to 1 at the same time. However, as soon as each of the qubits that makes up the result of the computation is read, the act of observing the qubit makes it stick in one of these two values. Retrieving the result of a quantum computation yields the result of only one of the many calculations that were performed. None of the other results remains accessible.
You may well ask what the use of the answer to a mathematical calculation is if there is no way of choosing the question. The crucial point is that some of the operations used in quantum computing can skew the probability with which each qubit has one or the other value. Such operations can be cleverly combined to make it likely that the result retrieved from a computation will be the answer to a specific question chosen by the programmer.
It may be helpful to compare the eight-qubit quantum computer with its classical counterpart and imagine it adding in parallel each of the members of a complete range of whole numbers between zero and fifteen to each of the members of a second, identical range of numbers. However, this analogy misrepresents the way quantum computing works.
In quantum computing, it is not just the storage of information that is revolutionary. The simplest building blocks that a classical computer uses when it runs a program are based on interactions between flows of electric current. A quantum computer, on the other hand, makes individual physical particles interact with one another in ways that are themselves unlike anything in our everyday experience. While it is certainly possible to write a quantum program to add two numbers, the steps that would be used to do so are completely different from the ones somebody programming a classical computer would have at their disposal.
In short, a quantum program is not just lots of classical programs operating in parallel. Because quantum computing and classical computing operate in totally dissimilar fashions, they tend to be good at different things. A quantum computer would not be an appropriate tool to solve the simple arithmetic at which classical computers excel, while the new mechanisms it offers can be exploited to achieve quick fixes for some mathematical problems that classical computers can only solve using brute-force methods. In many cases, these are the very mathematical problems on which today’s encryption standards are based.
It turns out that quantum computing would make cracking contemporary symmetric encryption methods easier, but that the advantage could be counterbalanced by doubling the number of bits used in each key to increase the number of possible values. For the asymmetric methods that use private / public keys, on the other hand, quantum computing would pose a much more serious problem. It would provide easy solutions to the mathematical problems on which all the current asymmetric standards are based. In the right circumstances, a quantum computer could allow its owner to find out other people’s private keys. The private / public encryption system would no longer serve its purpose.
Although practical research has certainly confirmed the theory behind quantum computing, none of the experimental quantum computers built so far have been able to use more than a very small number of qubits, nor have they worked well enough to be able to solve any mathematical problems more rapidly than the fastest classical computers. Nonetheless, it is probably only a matter of time until the remaining engineering problems are satisfactorily solved and the technology becomes mature enough for practical use.
New methods of encryption and decryption will probably emerge that can only be carried out using quantum technology. For the time being, however, the race is on to develop and standardise quantum-resistant asymmetric encryption techniques. These will be performed on classical computers just like the methods that are in use today. At the same time, they will rely on mathematical problems that a quantum computer would not be able to solve in a trivial fashion, which will provide assurance that the encodings they provide will not be open to analysis by quantum computers at some point in the future.
|Tweet about quantum encryption|
Next section: Government restrictions on encryption


But if we continue to follow the trend that has been in place since computers were introduced, by 2040 we will not have the capability to power all of the machines around the globe, according to a recent report by the Semiconductor Industry Association.
To prevent this, the industry is focused on finding ways to make computing more energy efficient, but classical computers are limited by the minimum amount of energy it takes them to perform one operation.
This energy limit is named after IBM Research Lab's Rolf Landauer, who in 1961 found that in any computer, each single bit operation must use an absolute minimum amount of energy. Landauer's formula calculated the lowest limit of energy required for a computer operation, and in March this year researchers demonstrated it could be possible to make a chip that operates with this lowest energy.
It was called a "breakthrough for energy-efficient computing" and could cut the amount of energy used in computers by a factor of one million. However, it will take a long time before we see the technology used in our laptops; and even when it is, the energy will still be above the Landauer limit.
This is why, in the long term, people are turning to radically different ways of computing, such as quantum computing, to find ways to cut energy use.
What is quantum computing?
Quantum computing takes advantage of the strange ability of subatomic particles to exist in more than one state at any time. Due to the way the tiniest of particles behave, operations can be done much more quickly and use less energy than classical computers.
In classical computing, a bit is a single piece of information that can exist in two states – 1 or 0. Quantum computing uses quantum bits, or 'qubits' instead. These are quantum systems with two states. However, unlike a usual bit, they can store much more information than just 1 or 0, because they can exist in any superposition of these values.
"Traditionally qubits are treated as separated physical objects with two possible distinguishable states, 0 and 1," Alexey Fedorov, physicist at the Moscow Institute of Physics and Technology told WIRED.
"The difference between classical bits and qubits is that we can also prepare qubits in a quantum superposition of 0 and 1 and create nontrivial correlated states of a number of qubits, so-called 'entangled states'."
A qubit can be thought of like an imaginary sphere. Whereas a classical bit can be in two states - at either of the two poles of the sphere - a qubit can be any point on the sphere. This means a computer using these bits can store a huge amount more information using less energy than a classical computer.
Advances in quantum computing
Last year, a team of Google and Nasa scientists found a D-wave quantum computer was 100 million times faster than a conventional computer. But moving quantum computing to an industrial scale is difficult.
IBM recently announced its Q division is developing quantum computers that can be sold commercially within the coming years. Commercial quantum computer systems "with ~50 qubits" will be created "in the next few years," IBM claims. While researchers at Google, in Nature comment piece, say companies could start to make returns on elements of quantum computer technology within the next five years.
Computations occur when qubits interact with each other, therefore for a computer to function it needs to have many qubits. The main reason why quantum computers are so hard to manufacture is that scientists still have not found a simple way to control complex systems of qubits.
Now, scientists from Moscow Institute of Physics and Technology and Russian Quantum Centre are looking into an alternative way of quantum computing. Not content with single qubits, the researchers decided to tackle the problem of quantum computing another way.
"In our approach, we observed that physical nature allows us to employ quantum objects with several distinguishable states for quantum computation," Fedorov, one of the authors of the study, told WIRED.
The team created qubits with various different energy "levels", that they have named qudits. The "d" stands for the number of different energy levels the qudit can take. The term "level" comes from the fact that typically each logic state of a qubit corresponds to the state with a certain value of energy - and these values of possible energies are called levels.
"In some sense, we can say that one qudit, quantum object with d possible states, may consist of several 'virtual' qubits, and operating qudit corresponds to manipulation with the 'virtual' qubits including their interaction," continued Federov.
"From the viewpoint of abstract quantum information theory everything remains the same but in concrete physical implementation many-level system represent potentially useful resource."
Quantum computers are already in use, in the sense that logic gates have been made using two qubits, but getting quantum computers to work on an industrial scale is the problem.
"The progress in that field is rather rapid but no one can promise when we come to wide use of quantum computation," Fedorov told WIRED.
Elsewhere, in a step towards quantum computing, researchers have guided electrons through semiconductors using incredibly short pulses of light.
Inside the weird world of quantum computers
These extremely short, configurable pulses of light could lead to computers that operate 100,000 times faster than they do today. Researchers, including engineers at the University of Michigan, can now control peaks within laser pulses of just a few femtoseconds (one quadrillionth of a second) long. The result is a step towards "lightwave electronics" which could eventually lead to a breakthrough in quantum computing.
Quantum computing and space
A bizarre discovery recently revealed that cold helium atoms in lab conditions on Earth abide by the same law of entropy that governs the behaviour of black holes.
What are black holes? WIRED explains
The law, first developed by Professor Stephen Hawking and Jacob Bekenstein in the 1970s, describes how the entropy, or the amount of disorder, increases in a black hole when matter falls into it. It now seems this behaviour appears at both the huge scales of outer space and at the tiny scale of atoms, specifically those that make up superfluid helium.
"It's called an entanglement area law,” explained Adrian Del Maestro, physicist at the University of Vermont. "It points to a deeper understanding of reality” and could be a significant step toward a long-sought quantum theory of gravity and new advances in quantum computing.


Single field shapes quantum
Technology Research News
computers, which tap the properties of particles like atoms, photons and
electrons to carry out computations, could potentially use a variety of
schemes: individual photons controlled by optical networks, clouds of atoms
linked by laser beams, and electrons trapped in quantum dots embedded in
Due to the strange nature of quantum particles, quantum computers
are theoretically much faster than ordinary computers at solving certain
large problems, like cracking secret codes.
Chip-based quantum computers would have a distinct advantage: the
potential to leverage the extensive experience and manufacturing infrastructure
of the semiconductor industry. Controlling individual electrons, however,
is extremely challenging.
Researchers have recently realized that it may be possible to control
the electrons in a quantum computer using a single magnetic field rather
than having to produce extremely small, precisely focused magnetic fields
for each electron.
Researchers from the University of Toronto and the University of
Wisconsin at Madison have advanced this idea with a scheme that allows individual
electrons to serve as the quantum bits that store and process computer information.
The scheme is an improvement over existing global magnetic field schemes,
which require each qubit to consist of two or more electrons.
Electrons have two magnetic orientations, spin up and spin down,
which can represent the 1s and 0s of computing. The logic of quantum computing
is based on one-qubit gates and two-qubit gates. One-qubit gates flip individual
spins, changing a 1 to a 0 and vice versa. Two-qubit gates cause two spins
to become linked, or entangled.
The researchers' scheme relies on the interactions of pairs of electrons
to create both types of gates. Tiny electrodes positioned near quantum dots
-- bits of semiconductor material that can trap single electrons -- can
draw neighboring electrons near enough that they exchange energy. If the
electrons interact long enough, they swap spin orientations. The challenge
is finding a way to use the interaction to flip the spin of one electron
without flipping the spin of the other.
The scheme does so by taking a pair of electrons through eleven
incremental steps using the electron interaction and the global magnetic
field. "We first turn on the exchange interactions... through small electrodes
to generate a swap gate, then turn on the global magnetic field," said Lian-Ao
Wu, a research associate at the University of Toronto.
The eleven steps -- four electron interactions and seven pulses
of the magnetic field -- alter the spins. Because the magnetic field diminishes
in strength over distance each electron is exposed to a different strength.
By tuning the field, the researchers can make the process cancel out the
changes to one spin while flipping the other, according to Wu.
The researchers' scheme could be implemented using a pair of square,
100-nanometer-diameter aluminum nanowires separated by a thin insulating
layer. A row of quantum dots in a zigzag pattern would be positioned parallel
to the wires, with half of the dots 200 nanometers from the wires and the
other half 300 nanometers away. A nanometer is one millionth of a millimeter,
or the span of 10 hydrogen atoms.
The ability to build such a quantum computer depends on developments
in nanotechnology, said Wu. "It is still hard to design a complete control
scheme of the exchange interactions," he said. "Once such obstacles are
overcome, our scheme should offer significant simplifications and flexibility."
The on-chip conducting wires called for in the researchers' scheme
have been used in physics experiments involving controlling beams of atoms
and Bose-Einstein condensates, which are small clusters of atoms induced
to behave as one quantum entity, according to Wu.
The researchers are working on reducing the number of steps required
for their quantum logic circuit, combining their scheme with quantum error
correction techniques, and reducing the engineering challenge of implementing
the design, said Wu. The scheme would require making the aluminum wires
with a precision of a single layer of atoms, but optimizing the scheme should
make it possible to loosen the requirements to several atomic layers, which
is technologically feasible, according to Wu.
"The main challenge is [achieving a] high degree of control of the
exchange interactions," he said.
The technique could be used practically in 10 to 20 years, said
Wu's research colleague was Daniel A. Lidar at the University of
Toronto and Mark Friesen at the University of Wisconsin at Madison. The
work appeared in the July 15, 2004 issue of Physical Review Letters.
The research was funded by the Defense Advanced Research Projects Agency
(DARPA), the National Science Foundation (NSF), and the Army Research Office/Advanced
Research and Development Activity (ARO/ARDA).
Timeline: 10-20 years
TRN Categories: Quantum Computing and Communications
Story Type: News
Related Elements: Technical paper, "One-Spin Quantum Logic
Gates from Exchange Interactions and a Global Magnetic Field," Physical
Review Letters, July 15, 2004
November 3/10, 2004
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Taking a Practical Step Forward in Optical Computing Using Slow Light: Photonic Crystals Offer a Slow Light Solution for Optical Computing
Previously published on Apr 13, 2011
Quantum computing is the Mount Everest of the information technology revolution. What approach succeeds will almost assuredly utilize optical components. With the limits of traditional electronics threatening to halt progress, alternatives, such as optical computing, will be needed in the not so distant future. One major hurdle for the development of such optical systems has been the need to convert between optical and electronic signals. Because time spent converting optical data into an electronic format takes longer than simply using the traditional medium, the concept is impractical in many respects. On the other hand, an almost paradoxical concept known as slow light offers a way around this barrier with a very practical solution.
It is a fundamental law of the universe that light can only exist at the speed of light. That is, photons must always move at approximately 300 million meters per second.
Looking closely at this law reveals a rather obvious loophole. Light waves passing through almost any given medium usually take longer to propagate through said medium than they would free space, because the light is bent along a lengthier path due to the internal properties of the medium. In other words, photons will continue to move at light speed, but it takes them longer to navigate through an object rather than simply moving within a vacuum at light speed, i.e. light goes slower. Consequently, given the proper medium, light could be slowed to a crawl, or even stopped.
It is how much a medium bends light that determines the "speed" of light and this property classically depends upon a material's index of refraction. A material with a high enough index of refraction, therefore, could be used to slow light. While the first demonstration of slow light in 1999, which yielded a speed around 17 meters per second, utilized a Bose-Einstein Condensate, which is a low-temperature state of matter where the atoms lose their individual characteristics and act almost as a single particle, one alternative approach is to utilize the many emerging manmade meta-materials that exhibit extreme properties, including super high indexes of refraction. On the other hand, researchers at the University of Sydney in New South Wales looked at advances in photonic crystals to suggest an even easier, more dynamic alternative.
Photonic crystals are a rapidly advancing technology first developed in the 1990's. By engineering regular structures in an optical material, light will respond to the pattern as though it is passing through a crystal. Giving researchers far greater control over light, photonic crystals can be used to slow light to variable speeds at continually shrinking costs with greater precision and less bulk. In fact, Professor Benjamin Eggleton's research group has already demonstrated an approach using a photonic crystal structure engineered by a University of St. Andrews team led by Professor Thomas F. Krauss for use over a broad bandwidth yields a sixteen fold increase in processing speeds over a traditional silicon chip, or 640 gigabits a second.
As such, it is obvious the next step forward is hybrid systems using photonic crystal chips. The key to processing and transmitting data stems from the ability to control how information flows. Light can get information to where it needs to go rather quickly, but the information must be stored until it can be used. Optical buffering as the "old fashion" approach relies on costly conversions between optical and electronic signals, so slowing light is a better option. If light is slowed or stopped until it is needed, a hybrid optical-electronic system would be extremely practical with results instantly surpassing the capacity of electronic devices. Consequently, we may soon see a major advancement in the telecommunications industry, followed by a renewed revolution in all computing technologies.
Thanks to initiatives for promoting civil investments in solar energy, LED lighting, national security and so on, technologies based on research from the fields of optics have known great progress in recent years. Just as the fruits of this research finally start to ripen, however, public support is drying up due to budget battles in Europe and the United States. Meanwhile, private funding can often be very selective to our civilization's detriment as entrepreneurs only want to invest in products that guarantee them a return, especially in the current environment where high return, low cost business deals can be exploited by the investment community. The US was already significantly behind in providing funds for research while even less funding is certain to retard progress just as we are the verge of major advances on a number of fronts.
With relatively low-cost experimental needs, the optical sciences offer solutions for everything from national and energy security to pharmaceutical and agricultural applications. Breakthroughs like slow light, meta-materials, photonic crystals, and quantum dots, which are essentially "traps" for photons and other particles, came about due to somewhat basic theories of some very complex subjects and scientists simply questioning. Not only do these discoveries and more have a myriad of potential applications, the costs associated with these technologies fall as we see progress while the benefits and profits begin to amass. Pursuing related research has already revealed some very meaningful discoveries and opportunities, but our society must be more aggressive in our pursuit of the basic research required to realize current and future gains.


Graphene is a honeycomb-like lattice made of a one-atom-thick layer of carbon atoms. It is the thinnest, lightest, and strongest known material and offers extremely high electrical and thermal conductivity. Recently, researchers are trying to add superconductivity to its unique set of properties.
How Does Superconductivity Happen?
A superconductor achieves zero electrical resistance below a certain temperature which may be as low as -269 degrees Celsius. Such superconductors, called low-temperature superconductors [PDF], were discovered nearly 100 years ago. On the other hand, high-temperature superconductors, which has a transition temperature of about -135 degree Celsius, were not discovered until about 30 years ago.
A low-temperature superconductor using liquid nitrogen. Photo courtesy of Camilla Hoel [CC BY-SA 2.0]
In a metal, electrons move on their own, repelling and colliding with each other. However, in a superconductor, they travel in pairs and move more smoothly. Suchitra Sebastian, an applied physicist at the University of Cambridge, envisions that in a superconductor electrons travel in lanes. Today, scientists have a deeper understanding of low-temperature superconductors. They know that the crystal structure of these materials forces the electrons to travel in pairs.
Applications of Superconductors
Magnetic levitation is one of the most well-known applications of superconducting where the strong superconducting magnets are used to make a vehicle, such as a train, float in the air and travel at extremely high speeds. In April 2015, the MLX01 test vehicle achieved an incredible speed of 603 kph.
The medical applications of superconductors are magnetic resonance imaging (MRI) and the SQUIDs. The latter can be used to examine certain depths of the body without applying a strong magnetic field like that of MRI. Another interesting application of this technology is superconductor-based electric generators which are estimated to have a worldwide market of $20-30 billion in the next decade.
Petaflop computers, ultra-high-performance filters, very low-frequency antennas, and E-bombs are just a few of other applications of this technology which would be impossible otherwise. Superconductivity was observed in graphite years ago and, even before experimental verifications, scientists believed that incorporating the right additives must lead to superconductivity in graphene.
Superconductivity of Lithium-Coated Graphene
Less than two years ago, researchers incorporated lithium atoms to make the world’s first graphene superconductor. The international research team created graphene sheets and coated them with lithium atoms.
Andrea Damascelli, director of the University of British Columbia's Quantum Matter Institute in Vancouver who was involved in this research, noted that the way samples are prepared is a key factor. Before this, several other groups had been trying to create superconducting lithium-coated graphene; however, they always faced sources of instability which made success elusive.
Damascelli and his colleagues experimented in ultra-high-vacuum conditions at about minus 268 degrees Celsius.
Calcium Atoms Sandwiched with Graphene Sheets
Nearly one year ago, researchers from Tohoku University and the University of Tokyo placed calcium atoms between sheets of graphene which were grown on a silicon carbide crystal. They achieved superconductivity at -269 degrees Celsius.
A representation of the developed material. Image courtesy of Tohoku University.
Obviously, these super cold temperatures are not suitable for applications such as superconductor-based power lines. However, according to Tohoku University, these studies pave the way for ultra high-speed superconducting nanodevices which can be used in quantum computing.
PCCO Unleashes the Superconductivity of Graphene
While the above experiments relied on doping graphene to achieve a superconductor, researchers from the University of Cambridge have recently developed a graphene-based superconductor without altering the material.
Jason Robinson, involved in the project, notes that, apparently, the study has achieved a rare type of superconductivity called p-wave state. However, he adds that further experiments are required to confirm this.
According to Angelo di Bernardo, methods which place graphene on other materials change its properties. On the other hand, although they achieve superconductivity, it is not necessarily from graphene but simply that of the underlying superconductor being passed on.
The Cambridge team incorporates a material called praseodymium cerium copper oxide (PCCO) to awaken graphene’s dormant superconductivity. While the experiment may look like previous ones where a second material was required to achieve superconductivity, the new method is quite different from previous techniques. In this recent experiment, the achieved superconductivity is clearly distinguished from that of the added material, i.e. PCCO. In a PCCO, electron pairs are in a state called d-wave; however, the spin state of electron pairs in the new superconductor was observed to be p-wave which is a rare and still unverified type of superconductivity first proposed by Japanese researchers in 1994.
According to Robinson, the superconductivity was not from PCCO and PCCO was simply required to unleash the intrinsic superconductivity of graphene.
The experiment is a big deal because it can prove that the elusive p-wave superconductivity really exists and, consequently, give the researchers the chance to properly investigate this type of superconductivity. With a better understanding of p-wave superconductivity, researchers may find a whole new spectrum of superconductors.
Uses for Superconducting Graphene
Superconducting graphene may not be a good choice to develop more efficient power lines, but researchers believe that it suits applications such as SQUIDs (superconducting quantum interference devices). SQUIDs, which are capable of sensing a change in a magnetic field over a billion times weaker than the force that moves the needle on a compass, can scan brain activities with a great precision.
Damascelli believes that graphene-based superconductors could lead to a 100-fold increase in the sensitivities which are currently achievable.
Unfortunately, there are many mysterious unknowns about how superconductivity is achieved in general, especially in graphene-based materials. However, all these endeavors seem to be quite rewarding and many research groups are intrigued to discover this territory.
The details of this research are published in Nature Communications.


A series of reports from the annual meeting of the American Association for the Advancement of Science kicks off with new developments in quantum computing
Feb 25th 2012 | vancouver | from the print edition
QUANTUM effects are vital to modern electronics. They can also be a damnable nuisance. Make a transistor too small, for example, and electrons within it can simply vanish from one place and reappear in another because their location is quantumly indeterminate. Currents thus leak away, and signals are degraded.
Other people, though, see opportunity instead. Some of the weird things that go on at the quantum scale afford the possibility of doing computing in a new and faster way, and of sending messages that—in theory at least—cannot be intercepted. Several groups of such enthusiasts hope to build quantum computers capable of solving some of the problems which stump today’s machines, such as finding prime factors of numbers with hundreds of digits or trawling through large databases. They gave a progress report to the annual meeting of the American Association for the Advancement of Science (AAAS) in Vancouver.
At the core of their efforts lie the quantum-mechanical phenomena of superposition and entanglement. An ordinary digital computer manipulates information in the form of bits, which take the value of either 0 or 1. These are represented within the computer as different voltages of electric current, itself the result of the electron’s charge. This charge is a fixed feature of all electrons; each has the same amount of it as any other. But electrons possess other, less rigid properties like spin, which can be either “up”, “down” or a fuzzy, imprecisely defined combination of the two. Such combinations, known as superpositions, can be used to construct a quantum analogue of the traditional bit—the qubit.
Entanglement, meanwhile, is the roping together of particles in order to add more qubits. Each extra qubit in a quantum machine doubles the number of simultaneous operations it can perform. It is this which gives quantum computing its power. Two entangled qubits permit four operations; three permit eight; and so on. A 300-qubit computer could perform more concurrent operations than there are atoms in the visible universe.
A coherent idea
Unfortunately, such a machine is not in the offing. Entanglement and superposition are delicate things. Even the slightest disturbance causes qubits to “decohere”, shedding their magical properties. To build a working quantum computer, qubits will have to become more resilient, and progress so far has been slow. The first quantum computations were done in the lab in 1995. Since then various teams have managed to entangle as many as 14 qubits. The record holders, a group in Innsbruck, use a device called an ion trap in which each qubit exists as a superposition of a rubidium atom at different energies. Raymond Laflamme and his colleagues at the University of Waterloo, in Canada, have managed to entangle 12 qubits by performing a similar trick, entangling certain atoms within a single molecule of an amino acid called histidine, the properties of which make it particularly suited to such experiments.
The problem with these approaches is that they will not be easy to scale up. Ion traps reside inside big vacuum chambers, which cannot easily be shrunk. And a molecule of histidine contains only so many suitable atoms. So the search is on for more practical qubits.
One promising approach is to etch qubits in semiconductors. Charles Marcus, previously of Harvard University and now at the University of Copenhagen, has been using electrons’ spins to do this. Single-electron qubits decohere quickly, so his team decided instead to create a qubit out of two electrons, which they trapped in “quantum dots”, tiny semiconducting crystals (of gallium arsenide, in this case). When two such dots are close together, it is possible to get an electron trapped in one to pop over and join its neighbour in the other. The superposition of the two electrons’ spins produces the qubit.
Dr Marcus’s team have so far managed to stitch four such qubits together. An array of clever tricks has extended their life to about ten microseconds—enough to perform the simple algebraic operations that are the lifeblood of computing. They hope to extend their life further by using silicon or carbon, the atomic nuclei of which interfere less with the entangled electrons than do those of gallium arsenide.
John Martinis and his colleagues at the University of California, Santa Barbara (UCSB), meanwhile, have been trying to forge qubits from superconducting circuits. In a superconductor, electrons do not travel solo. Instead, for complicated quantum-mechanical reasons, they pair up (for the same reasons, the pairs feel no electrical resistance). When they do so, the pairs start behaving like a single particle, superposing proclivities and all. This superparticle can, for instance, in effect be moving in two directions at once. As electrons move, they create a magnetic field. Make a closed loop of superconducting wire, then, and you get a magnetic field which can be facing up and down at the same time. You have yourself a superconducting qubit—or five, the number Dr Martinis has so far managed to entangle.
He has another clever trick up his sleeve. Using a device called a resonator he has been able to transfer information from the circuit to a single photon and trap it in a cavity for a few microseconds. He has, in other words, created a quantum memory. A few microseconds may not sound much, but it is just about enough to perform some basic operations.
The problem with all these approaches is that the quantum states they rely on are fragile, which allows errors to creep in. One way to ensure that they do not scupper the calculation is to encode the same information in several qubits instead of just one. Drs Marcus, Martinis and Laflamme have therefore had to build redundant qubits into their systems. For every “logical” qubit needed to do a calculation, there is a handful of physical ones, all of which need to be entangled.
Michael Freedman is trying to address this problem by taking a different tack. Together with his colleagues at Microsoft’s Station Q research centre, also at UCSB, he is trying to build what he calls a topological quantum computer. This uses a superconductor on top of a layer of an exotic material called indium antimony. When a voltage is applied to this sandwich, the whole lot becomes a quantum system capable of existing in superposed states.
Where Dr Freedman’s qubits differ from Dr Martinis’s is in the way they react to interference. Nudge any electron in a superconducting circuit and the whole lot decoheres. Dr Freedman’s design, however, is invulnerable to such local disruptions thanks to the peculiar way in which energy is distributed throughout indium antimony. The Microsoft team has yet to create a functioning qubit, but hopes to do so soon, and is searching for other materials in which to repeat the same trick.
All of this work is pretty fundamental. Researchers are a long way from creating quantum mainframes, which is how most of them see the future of their fiddly devices, let alone quantum desktops. Dr Martinis thinks that a viable quantum processor is still ten years away. Yet even this is progress of a sort. When he entered the field two decades ago, he thought that building a quantum processor was “insanely difficult”. Now he says it is merely “very, very hard”.
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It's a machine that could calculate solutions to problems so impossibly time-consuming that even the most powerful supercomputers could never handle them. And it would do so in an instant. This is the quantum computer, made possible by the bizarre nature of quantum mechanics. And though the idea is still in its infancy, it's no fantasy.
Two research teams, at Harvard University and the Max Planck Institute of Quantum Optics in Germany, have just announced that they have independently forged the building blocks for tomorrow's quantum computers. As they published today in the journal Nature (1, 2), the scientists discovered a way to hook up atoms and particles of light to create a new type of switch and logic-gate‚ quantum versions of the connecting structures that link bits of data in modern computers.
When you dive down into the circuits, all modern computers are basically the same: a huge collection of data arranged with simple rules. Each piece of data is called a bit and shows just one fragment of information‚ a 0 or a 1. You can think of a bit as a lightbulb that's either shining or not.
But quantum theory‚ the physics that rules the tiny world of atoms and particles‚ tells us that there are certain circumstances in which a piece of matter can be two things at the same time. It's possible to have an atom that's spinning in two opposite directions at once, or even to have your lightbulb both shining and not shining. Items with this wacky dual state are said to be in "superposition." (Physicist Niels Bohr once said, "Those who are not shocked when they first come across quantum theory cannot possibly have understood it." So don't worry if you're confused‚ Bohr was one of the founders of quantum theory.)
The most important catch (there are plenty) is that this superposition state is fragile and possible only for incredibly tiny bits of matter.
But for computers, this very idea poses an interesting prospect. If you could somehow harness this odd state of matter to put individual bits of information into superposition, then suddenly you've packed more data into the tiniest package possible. Your bits can now show a 0, a 1, or a combo of both. This is called a quantum bit, or a qubit. And if qubits were linked together like normal bits are linked in a computer, then you'd have a machine could calculate at insane speeds.
"At this point, very small-scale quantum computers already exist," says Mikhail Lukin, the head of the Harvard research team. "We're able to link, roughly, up to a dozen qubits together. But a major challenge facing this community is scaling these systems up to include more and more qubits."
The problem of adding more qubits, Lukin explains, is tied to the fragility of the superposition state. Unless the entire quantum computer is kept at extremely cold temperatures and free of any interfering particles or other noise, the superposition state will entirely collapse for all the qubits, ruining the computer. What makes this even harder is that today's qubits must be close to one another to be connected, and it takes a massive apparatus of machinery, lab equipment, and lasers to support the superposition state of just a single fleck of matter. That dumps an increasing amount of grit into the system, increasing the chance that the entire quantum computer will fail.
"It's just very difficult to address one qubit without interfering with all the rest of them; to take a laser beam and shine it one particular qubit and not another," says Gerhard Rempe, the head of the Max Planck Institute of Quantum Optics research team. "And if, for example, you want to use 10,000 qubits, well, that's 10,000 lasers you have to worry about."
The Ol' Gate and Switch
The new quantum logic gate and switch unveiled today promise to ameliorate some of these problems. Both use a new method: They harness trapped atoms (in both cases, rubidium) that can transfer information through photons, the particles that make up light. Photons, which can be directed through fiber-optic cable, are the prime candidate for sending information at great distances and keeping qubits apart.
Here is how it works: The scientists trap a heavy rubidium atom between two mirror-like sheets using a laser technique that keeps the atom relatively immobile. The scientists then send a photon straight at this atom sandwich. Normally, the photon would hit the first mirror and bounce right back where it came from. But if the atom is put in a specific energetic state, the photon will go straight through that first mirror, hang out with the atom for a moment, and then exit where it came from. As a going-away present, the photon also has a slight change in polarization. This is pretty much how any switch in a computer works. If something is "on," then one thing happens. If it's "off," then another thing happens.
But here's the tricky part. The scientists can put the rubidium atom in superposition, so that it is simultaneously in that energetic state and not in the energetic state. It's on and off. Because of this, the photon both does and does not enter the mirror, mingle, and gain its polarization change. And the photon, by virtue of having both changed and not changed, carries that superposition information and can bring it to a different atom-based qubit.
A similar process happens with the quantum logic gate. A normal logic gate is just a series of switches set up in a way that together, they perform a logical operation when given multiple inputs. The German team created a quantum version by having multiple photons repeatedly bounce off the mirror-trapped and superpositioned rubidium atom. Then, using another funky attribute of quantum physics called entanglement swapping, the scientists made it so that the photons share the same information. These entangled photons can become the multiple inputs required for any logic gate.
Even with this new advancement, we're still a long way from building large-scale quantum computers, with thousands of qubits linked together. "We're not going to see quantum computers being built for the average American consumer in ten years, or anything like that," says Jeff Thompson, a physicist with the Harvard research team.
Rempe says that while this technology seems promising for solving the qubit-closeness issue, neither team is actually attempting to link multiple qubits. And that endeavor will probably open up a new world of unknowns.
Nonetheless, "It's exciting to see this [photon-based] technology is coming into its own," says Jacob Taylor, a physicist at the University of Maryland who was not involved with the projects. Whatever future difficulties arise, he says, scientists are learning valuable information about one of the most fundamental aspects of physics. Everything we know about quantum mechanics would lead us to believe that large-scale quantum computers should be theoretically possible. But even if "you couldn't build a large-scale quantum computer," he says, "that's somewhat exciting, too. That tells us that our theory of quantum mechanics might be breaking down somewhere, that we still have much to learn."


Some people want to move mountains. Kunal Das, Ph.D., assistant professor of physics, wants to move electrons.
Das is a theoretical physicist researching an area where the classical rules of physics no longer apply—the nanoscale universe of quantum physics, a submicroscopic world where particles defy common sense. In that mysterious world of the ultra-small, Das is searching for new ways to move the currents that power computers.
“When the first computers came along in the 1960s, they were huge objects which filled up an entire room and had miniscule computing power,” Das says, as he gestures to his computer in his Freeman Hall office. “How is it that today we have something this compact and with this much more power? Today, every two years computers become twice as fast and half as big.”
Computers are powered by electronic circuitry in which currents move large clusters of electrons at a time to feed a tiny computer chip. The number of electrons needed for each operation has gotten smaller with time. But within 20 years, Das says, computers will reach a point where each operation could be done by just one electron, and thus won’t be able to get any faster or any smaller.
What then? Where will technology go?
Already, scientists are experimenting with storing information not in bits, but in qubits (or quantum bits), which can potentially store much larger amount of information than traditional bits. Can a “quantumchip” be in the offing?
That’s where quantum mechanics come in.
Das has focused his research on adiabatic electron pumps, which can be used to control the flow of individual or entangled pairs of electrons in order to power quantum computers. Quantum computers, which are still in their infancy, have the potential to perform certain calculations significantly faster than any silicon-based computer.
Quantum mechanics have become very important partly because, at the qubit level, individual particles of matter play essential roles. The current that powers the computer no longer flows as a cluster of electrons, but as one electron at a time; and such motion is governed by quantum mechanics.
“In classical physics, we talk about currents flowing continuously, like water,” Das says. “At the nanoscale, your current is comprised of individual electrons, and it is discrete as opposed to continuous.”
In other words, if you were to look at water flowing through a pipe, you would discover that at the submicroscopic level it is made of molecules that are discrete from one another, like individual grains of sand.
The problem is that the super-small world of quantum mechanics is notoriously unpredictable. In fact, an electron at the quantum level has a few weird characteristics that stem from the fact that quantum mechanics is all about probabilities, not absolutes.
“An electron, from a quantum mechanical perspective, does not behave like it does in classic physics, where it always acts like a particle,” Das says. “Here, it acts like a particle some of the time and like a wave some of the time. It has wave-particle duality, and it becomes probabilistic, meaning you cannot say for sure that the electron is definitely here. It might have some probability of it being here, or some probability of it being there. That’s what makes quantum mechanics strange and confusing to the layperson.”
An adiabatic electron pumping system is complex, but Das describes it as a mechanism that manipulates the shape of the “quantum wavefunction” of an electron, by varying such things as voltage or a magnetic field at the nanoscale. Das is researching how to apply the pumping system to single electrons and also to pairs of “entangled” electrons in which one electron can affect another even when separated by vast distances.
He hopes that his research will ultimately lead to a dependable system of moving currents of electrons in a precisely controlled way without destroying their fragile quantum state, which is essential to powering quantum computers.
“Once we start using the wave nature of electrons and the probabilistic nature of quantum mechanics, we can potentially do certain computations tremendously faster,” he says.
At this point, quantum computers have not yet been built, although some experiments have been carried out. Research is being done at a frantic pace, however, as such systems would be invaluable to national security, Das says.
“All existing encryption systems are based upon the fact that we cannot crack them with the computers that we have available now,” says Das. “With a quantum mechanical algorithm, you could crack encryption methods very fast.”
There are also potential applications to teleportation, Das says, but not of the Star Trek variety—at least not yet.
What you could teleport is the state of an electron,” he says. “We could transfer those properties to a location which is far away, but not the physical object itself. So, in a sense, in quantum mechanics, you can be in two places at the same time.”


Quantum computers should be much easier to build than previously thought, because they can still work with a large number of faulty or even missing components, according to a study published today in Physical Review Letters. This surprising discovery brings scientists one step closer to designing and building real-life quantum computing systems - devices that could have enormous potential across a wide range of fields, from drug design, electronics, and even code-breaking.
Scientists have long been fascinated with building computers that work at a quantum level - so small that the parts are made of just single atoms or electrons. Instead of 'bits', the building blocks normally used to store electronic information, quantum systems use quantum bits or 'qubits', made up of an arrangement of entangled atoms.
Materials behave very differently at this tiny scale compared to what we are used to in our everyday lives - quantum particles, for example, can exist in two places at the same time. "Quantum computers can exploit this weirdness to perform powerful calculations, and in theory, they could be designed to break public key encryption or simulate complex systems much faster than conventional computers," said Dr Sean Barrett, the lead author of the study, who is a Royal Society University Research Fellow in the Department of Physics at Imperial College London.
The machines have been notoriously hard to build, however, and were thought to be very fragile to errors. In spite of considerable buzz in the field in the last 20 years, useful quantum computers remain elusive.
Barrett and his colleague Dr. Thomas Stace, from the University of Queensland in Brisbane, Australia, have now found a way to correct for a particular sort of error, in which the qubits are lost from the computer altogether. They used a system of 'error-correcting' code, which involved looking at the context provided by the remaining qubits to decipher the missing information correctly.
"Just as you can often tell what a word says when there are a few missing letters, or you can get the gist of a conversation on a badly-connected phone line, we used this idea in our design for a quantum computer," said Dr Barrett. They discovered that the computers have a much higher threshold for error than previously thought - up to a quarter of the qubits can be lost - but the computer can still be made to work. "It's surprising, because you wouldn't expect that if you lost a quarter of the beads from an abacus that it would still be useful," he added.
The findings indicate that quantum computers may be much easier to build than previously thought, but as the results are still based on theoretical calculations, the next step is to actually demonstrate these ideas in the lab. Scientists will need to devise a way for scaling the computers to a sufficiently large number of qubits to be viable, says Barrett. At the moment the biggest quantum computers scientists have built are limited to just two or three qubits.
"We are still some way off from knowing what the true potential of a quantum computer might be, says Barrett. "At the moment quantum computers are good at particular tasks, but we have no idea what these systems could be used for in the future," he said. "They may not necessarily be better for everything, but we just don't know. They may be better for very specific things that we find impossible now."
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2 "Fault tolerant quantum computation with very high threshold for loss errors"
Physical Review Letters 09 November 2010, to be published online at:
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Link to paper on pre-print server: http://arxiv.
Corresponding author: Sean Barrett, Institute for Mathematical Sciences, Imperial College London.
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Credit: Sean Barrett and Thomas Stace.
Caption: Illustration of the error correcting code used to demonstrate robustness to loss errors. Each dot represents a single qubit. The qubits are arranged on a lattice in such a way that the encoded information is robust to losing up to 25 percent of the qubits
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Quantum Computation with Trapped Ions
Today computers are indispensable even in our daily life. Each year engineers create more powerful computers simply by making them smaller. Can this continue for ever? With the current rate of miniaturization in about 20 years single atoms will be used for storage and manipulation of information. For such small objects, however, our usual intuition fails, since they do not follow classical, but quantum mechanical rules. Is it still possible to build a computer based on these strange, new quantum laws?
Already in 1982, Richard Feynman pronounced the idea that certain calculations could be performed much more efficiently with quantum mechanical than with classical computers. In 1994, the first computational problem was proved to be solvable substantially faster with a "quantum algorithm" (the Shor algorithm) compared to a classical one. Nevertheless, the physics and mathematics behind this is little known to most people, and experimental exploration of this fascinating subject has just started. Our approach is based on well controlled laser beams and a series of calcium ions, confined to a space of less than a hair wide.
Linear ion trap: By applying voltages to the trap electrodes, a string of ions
can be held in the trap for several days. The lower picture shows a string
of 6 Calcium 40 ions taken with a ordinary CCD camera.
Our group has demonstrated the basic principles of such a quantum computer. Currently, we are working with up to eight ionized Calcium atoms suspended in free space by electromagnetic forces. Each atom represents one quantum bit (qubit). In contrast to classical bits, a qubit can take any value between 0 and 1, so that it contains partially both values at the same time. Due to this property it is possible to calculate an algorithm for both values in parallel. Thus loosely speaking, quantum computers can solve different tasks simultaneously. For certain tasks - like simulation of complicated quantum processes - even a 40-bit quantum computer would be much more powerful than any existing classical computer.
Sketch of the experimental setup. The quantum state of the trapped ions is manipulated
by laser pulses and finally detected by measuring the ion's fluorescence on a CCD camera.
Absence and presence of fluorescence signal the qubit's "0" and "1" states, respectively.
In our prototype quantum computer, we use lasers to manipulate quantum information encoded in the atoms. The atomic states evolve according to the chosen strength and frequency of the laser pulse. Also, lasers serve to read out the qubits: depending on their state, the atoms either emit light or remain dark which can be readily detected with a CCD-camera. One of the biggest challenges is to control the interaction between these tiny quantum bits. Similarly to classical computing, for quantum computers there exists a small set of (quantum) gates with which every quantum algorithm can be realized. Using two trapped ions, we have demonstrated an important quantum gate, the controlled-NOT operation (F. Schmidt-Kaler et al.) which - together with single qubit gates - constitutes such a set of gates. We have realized the quantum mechanical equivalent to the Toffoli gate - a controlled-controlled-NOT gate (T. Monz et al.). This gate could become an essential element for implementing quantum error correction (QEC).
Exploring quantum physics
Quantum computing techniques are also very useful tools for exploring the strange rules of quantum physics. We have created entangled states of up to eight ions (H. Häffner et al.). Here, the state of a single particle is completely undetermined even though the state of the whole system is well-defined. These states are used to investigate fundamental properties of quantum physics like, for example, the collapse of the wave function induced by measurements. Also, we can demonstrate the non-local nature of quantum theory, i.e. the fact that the quantum state of an object can be inextricably linked to the quantum state of another (distant) object. This property plays a key role in quantum state teleportation.
A closer look at the quantum computing setup showing a box of mu-metal for magnetic shielding, inside the vacuum vessel housing the ion trap and laser beam steering optics around.
Quantum teleportation with ions
Quantum state teleportation is a scheme that solves the task of transferring an unknown quantum state from one location to another. First achieved with entangled photons, it is also applicable to atomic quantum states. In our implementation (M. Riebe et al.) based on three ions, we show that the quantum information encoded in one ion is deterministically transferred to another ion at any time. Although the teleportation distance is currently limited to 10 micrometers, the development of segmented ion traps with complex electrode structures will overcome this limitation and increase the distance over which quantum information can be communicated.
Schematic of the teleportation of a quantum state.
Entanglement swapping with ions
A similar protocol as for quantum teleportation can be used to entangle two ions that have never interacted before. Such deterministic entanglement swapping (M. Riebe et al.) was recently show by our group (C. F. Roos et al. and H. Häffner et al.). Entanglement swapping is of particular significance for the next generation of quantum computers where it could be used to entangle and link qubits in distant regions of the quantum processor.
Quantum computation with logical qubits
A quantum computer can encode logical information in superpositions of quantum states. The information is contained in the relative probabilities of the two states of the qubits, but also their respective phase. Environmental effects like magnetic field fluctuations or laser instabilities can result in dephasing, and therefore loss, of quantum information. However, special states - the so called decoherence free subspace (DFS) - are insensitive to dephasing. We have shown encoding of qubits within that subspace (M. Chwalla et al.), storing information in a way that is only limited by the lifetime of the qubit states. Currently, we are working on techniques to use such robust encoding for calculating arbitrary algorithms
View into the vacuum chamber with the ion trap inside.
(Lintrap Group picture)
- Roman Stricker (Master's student)
- Alexander Erhard (PhD student)
- Esteban Martinez (PhD student)
- Daniel Nigg (PhD student)
- Thomas Monz (Postdoc)
- Philipp Schindler (project leader)
- Rainer Blatt (group leader)
Former members: Julio Barreiro, Michael Chwalla, Stefan Quint


Study of electron movement on helium may impact the future of quantum computing
Images of the electron trap architecture. Top: Schematic representation of the experiment. Current of surface electrons, induced by ac voltage applied to the electrode underneath Reservoir 1, flows between Reservoirs 1 and 4, as shown by the red arrow. Middle: Cross section of the central microchannel around the gate area. Bottom: Photograph of the microchannel device on a copper sample cell, with subsequent close-up photographs of the central channel and surrounding reservoirs.Credit: Denis Konstantinov
The future of quantum computing is a hot topic not only for experts but also in many commercial and governmental agencies. Rather than processing and storing information as bits in transistors or memories, which limit information to the binary ‘1’ or ‘0’, quantum computers would instead use quantum systems, such as atoms, ions, or electrons, as ‘qubits’ to process and store “quantum information” in, which can be in an infinite number of combinations of ‘1 and 0’. Large technology corporations, such as Google, Microsoft, Intel, and IBM are investing heavily in related projects that may lead to realize the quantum computer and technologies. At the same time, universities and research institutes around the world are researching novel quantum systems, adoptable for quantum computing.
The Quantum Dynamics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST), has recently made novel findings about electrons floating on the surface of liquid helium, a quantum system which may be a new candidate for quantum computing into reality. These results were published in Physical Review B.
One of the common problems in quantum computing research using solids is that it is very difficult to make perfectly identical qubits because intrinsic defects or impurities in the materials used randomly affect each individual qubit performance. “Our motivation for pursuing a liquid helium system is that it is intrinsically pure and free of defects, which theoretically allows for the creation of perfectly identical qubits. Additionally, we can move electrons in this liquid helium system, which is difficult or nearly impossible in other quantum systems,” explained Prof. Denis Konstantinov, head of the Quantum Dynamics Unit. Therefore, it is believed that adopting this system for quantum computing might bring the whole field to the next level.
Utilizing electrons on a liquid helium surface for quantum computing requires isolating individual electrons on a helium surface and controlling their quantum degrees of freedom, either motional or spin. It may also require the movement of electrons to different locations, thus it is also important to understand the physics of the interaction between electrons and the helium surface. It was previously discovered that electrons on helium can form a two-dimensional crystal, and some unique phenomena occur when this crystal moves along the helium surface, due to the interaction between electrons and surface waves.
The OIST scientists, however, are the first to probe how these phenomena depend on the size of the electron crystal. To test this, Dr. Alexander Badrutdinov, Dr. Oleksandr Smorodin and OIST PhD student Jui-Yin Lin, built a microscopic channel device that contained an electron trap within to isolate a crystal of a relatively small number of electrons. This crystal would then be moved across the liquid helium surface by altering electrostatic potential of one of the device electrodes. This motion would be detected by measuring image charges, which are induced by the moving electrons, flowing through another electrode using a commercially available current amplifier and lock-in detector. “This research gave us some insights into the physics of the interaction between electrons and the helium surface, as well as expanded our micro-engineering capabilities” states Dr. Alexander Badrutdinov, a former member of the Quantum Dynamics Unit and the first author of the paper. “We successfully adopted a technology to confine electrons into microscopic devices, on the scale of few microns. With this technology we studied the motion of microscopic two-dimensional electron crystals along a liquid helium surface and saw no difference between the movement of large electron crystals, on the scale of millions to billions of electrons, and crystals as small as a few thousands of electrons, when theoretically, differences should exist.”
This research is the first step at OIST in the prospect of using this system for quantum computing. According to Konstantinov, “the next step in this research is to isolate an even smaller electron crystal, and ultimately, a single electron, and to move them in this system. Unlike other systems, this system has the potential to be a pure, scalable system with mobile qubits.” In theory, this type of system would have the potential to revolutionize the quantum computing research field.
A.O. Badrutdinov, A. V. Smorodin, D. G. Rees, J. Y. Lin, D. Konstantinov. Nonlinear transport of the inhomogeneous Wigner solid in a channel geometry. Physical Review B, 2016; 94 (19) DOI: 10.1103/PhysRevB.94.195311