Thursday, October 30, 2014

Academics are Challenging The Foundations of Quantum Science

New quantum theory is out of this parallel world

Griffith University academics are challenging the foundations of quantum science with a radical new theory based on interactions between parallel universes.

[caption id="attachment_462" align="aligncenter" width="468"]Academics are Challenging The Foundations of Quantum Science The Director of Griffith’s Centre for Quantum Dynamics,                              Professor Howard Wiseman[/caption]

In a paper published in the prestigious journal Physical Review X,Professor Howard Wiseman and Dr Michael Hall from Griffith’sCentre for Quantum Dynamics, and Dr Dirk-Andre Deckert from the University of California, take interacting parallel worlds out of the realm of science fiction and into that of hard science.

The team proposes that parallel universes really exist, and that they interact. That is, rather than evolving independently, nearby worlds influence one another by a subtle force of repulsion. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Quantum theory is needed to explain how the universe works at the microscopic scale, and is believed to apply to all matter. But it is notoriously difficult to fathom, exhibiting weird phenomena which seem to violate the laws of cause and effect.

As the eminent American theoretical physicist Richard Feynman once noted: “I think I can safely say that nobody understands quantum mechanics.”

However, the “Many-Interacting Worlds” approach developed at Griffith University provides a new and daring perspective on this baffling field.

“The idea of parallel universes in quantum mechanics has been around since 1957,” says Professor Wiseman.

“In the well-known “Many-Worlds Interpretation”, each universe branches into a bunch of new universes every time a quantum measurement is made. All possibilities are therefore realised – in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese.

“But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our “Many Interacting Worlds” approach is completely different, as its name implies.”

Professor Wiseman and his colleagues propose that:

  • The universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different;

  • All of these worlds are equally real, exist continuously through time, and possess precisely defined properties;

  • All quantum phenomena arise from a universal force of repulsion between ‘nearby’ (i.e. similar) worlds, which tends to make them more dissimilar.

Dr Hall says the “Many-Interacting Worlds” theory may even create the extraordinary possibility of testing for the existence of other worlds.

“The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics,” he says.

“In between it predicts something new that is neither Newton’s theory nor quantum theory.

“We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena.”

The ability to approximate quantum evolution using a finite number of worlds could have significant ramifications in molecular dynamics, which is important for understanding chemical reactions and the action of drugs.

Professor Bill Poirier, Distinguished Professor of Chemistry at Texas Tech University, has observed: “These are great ideas, not only conceptually, but also with regard to the new numerical breakthroughs they are almost certain to engender.”

From chemistry to quantum physics to science fiction, this theory opens new and exciting territory.

Go to:

News Release Source :  New quantum theory is out of this parallel world

Image Credit : Centre for Quantum Dynamics, Griffith University

Wednesday, October 29, 2014

New Research Suggests The Electron's Quantum State Separated into Parts

Can the wave function of an electron be divided and trapped?

Electrons are elementary particles — indivisible, unbreakable. But new research suggests the electron's quantum state — the electron wave function — can be separated into many parts. That has some strange implications for the theory of quantum mechanics.

PROVIDENCE, R.I. [Brown University] 28/10/2014

New research by physicists from Brown University puts the profound strangeness of quantum mechanics in a nutshell — or, more accurately, in a helium bubble.

[caption id="attachment_456" align="aligncenter" width="580" class=" "]New Research Suggests The Electron's Quantum State Separated into Parts The electron wave function
A canister of liquid helium inside the blue cylinder allowed researchers to experiment with tiny electron bubbles only 3.6 nanometers in diameter. The work suggests that the wave function of an electron can be split and parts of it trapped in smaller bubbles.[/caption]

Experiments led by Humphrey Maris, professor of physics at Brown, suggest that the quantum state of an electron — the electron’s wave function — can be shattered into pieces and those pieces can be trapped in tiny bubbles of liquid helium. To be clear, the researchers are not saying that the electron can be broken apart. Electrons are elementary particles, indivisible and unbreakable. But what the researchers are saying is in some ways more bizarre.

In quantum mechanics, particles do not have a distinct position in space. Instead, they exist as a wave function, a probability distribution that includes all the possible locations where a particle might be found. Maris and his colleagues are suggesting that parts of that distribution can be separated and cordoned off from each other.

“We are trapping the chance of finding the electron, not pieces of the electron,” Maris said. “It’s a little like a lottery. When lottery tickets are sold, everyone who buys a ticket gets a piece of paper. So all these people are holding a chance and you can consider that the chances are spread all over the place. But there is only one prize — one electron — and where that prize will go is determined later.”

If Maris’s interpretation of his experimental findings is correct, it raises profound questions about the measurement process in quantum mechanics. In the traditional formulation of quantum mechanics, when a particle is measured — meaning it is found to be in one particular location — the wave function is said to collapse.

“The experiments we have performed indicate that the mere interaction of an electron with some larger physical system, such as a bath of liquid helium, does not constitute a measurement,” Maris said. “The question then is: What does?”

And the fact that the wave function can be split into two or more bubbles is strange as well. If a detector finds the electron in one bubble, what happens to the other bubble?

"It really raises all kinds of interesting questions," Maris said.

The new research is published in the Journal of Low Temperature Physics.

Electron bubbles

Scientists have wondered for years about the strange behavior of electrons in liquid helium cooled to near absolute zero. When an electron enters the liquid, it repels surrounding helium atoms, forming a bubble in the liquid about 3.6 nanometers across. The size of the bubble is determined by the pressure of the electron pushing against the surface tension of the helium. The strangeness, however, arises in experiments dating back to the 1960s looking at how the bubbles move.

In the experiments, a pulse of electrons enters the top of a helium-filled tube, and a detector registers the electric charge delivered when electron bubbles reach the bottom of the tube. Because the bubbles have a well-defined size, they should all experience the same amount of drag as they move, and should therefore arrive at the detector at the same time. But that’s not what happens. Experiments have detected unidentified objects that reach the detector before the normal electron bubbles. Over the years, scientists have cataloged 14 distinct objects of different sizes, all of which seem to move faster than an electron bubble would be expected to move.

“They’ve been a mystery ever since they were first detected,” Maris said. “Nobody has a good explanation.”

Several possibilities have been proposed. The unknown objects could be impurities in the helium—charged particles knocked free from the walls of the container. Another possibility is that the objects could be helium ions — helium atoms that have picked up one or more extra electrons, which produce a negative charge at the detector.

But Maris and his colleagues, including Nobel laureate and Brown physicist Leon Cooper, believe a new set of experiments puts those explanations to rest.

New experiments

The researchers performed a series of electron bubble mobility experiments with much greater sensitivity than previous efforts. They were able to detect all 14 of the objects from previous work, plus four additional objects that appeared frequently over the course of the experiments. But in addition to those 18 objects that showed up frequently, the study revealed countless additional objects that appeared more rarely.

In effect, Maris says, it appears there aren’t just 18 objects, but an effectively infinite number of them, with a “continuous distribution of sizes” up to the size of the normal electron bubble.

“That puts a dagger in the idea that these are impurities or helium ions,” Maris said. “It would be hard to imagine that there would be that many impurities, or that many previously unknown helium ions.”

The only way the researchers can think of to explain the results is through “fission” of the wave function. In certain situations, the researchers surmise, electron wave functions break apart upon entering the liquid, and pieces of the wave function are caught in separate bubbles. Because the bubbles contain less than the full wave function, they’re smaller than normal electron bubbles and therefore move faster.

In their new paper, Maris and his team lay out a mechanism by which fission could happen that is supported by quantum theory and is in good agreement with the experimental results. The mechanism involves a concept in quantum mechanics known as reflection above the barrier.

In the case of electrons and helium, it works like this: When an electron hits the surface of the liquid helium, there’s some chance that it will cross into the liquid, and some chance that it will bounce off and carom away. In quantum mechanics, those possibilities are expressed as part of the wave function crossing the barrier, and part of it being reflected. Perhaps the small electron bubbles are formed by the portion of the wave function that goes through the surface. The size of the bubble depends on how much wave function goes through, which would explain the continuous distribution of small electron bubble sizes detected in the experiments.

The idea that part of the wave function is reflected at a barrier is standard quantum mechanics, Cooper said. “I don’t think anyone would argue with that,” he said. “The non-standard part is that the piece of the wave function that goes through can have a physical effect by influencing the size of the bubble. That is what is radically new here.”

Further, the researchers propose what happens after the wave function enters the liquid. It’s a bit like putting a droplet of oil in a puddle of water. “Sometime your drop of oil forms one bubble,” Maris said, “Sometimes it forms two, sometimes 100.”

There are elements within quantum theory that suggest a tendency for the wave function to break up into specific sizes. By Maris’s calculations, the specific sizes one might expect to see correspond roughly to the 18 frequently occurring electron bubble sizes.

“We think this offers the best explanation for what we see in the experiments,” Maris said. We’ve got this body of data that goes back 40 years. The experiments are not wrong; they’ve been done by multiple people. We have a tradition called Occam’s razor, where we try to come up with the simplest explanation. This, so far as we can tell, is it.”

But it does raise some interesting questions that sit on the border of science and philosophy. For example, it’s necessary to assume that the helium does not make a measurement of the actual position of the electron. If it did, any bubble found not to contain the electron would, in theory, simply disappear. And that, Maris says, points to one of the deepest mysteries of quantum theory.

“No one is sure what actually constitutes a measurement. Perhaps physicists can agree that someone with a Ph.D. wearing a white coat sitting in the lab of a famous university can make measurements. But what about somebody who really isn’t sure what they are doing? Is consciousness required? We don’t really know.”

Authors on the paper in addition to Maris were former Brown postdoctoral researcher Wanchun Wei, graduate student Zhuolin Xie, and George Seidel, professor emeritus of physics.

News Release Source : Can the wave function of an electron be divided and trapped?

Image Credit : Mike Cohea/Brown University

Thursday, October 23, 2014

American Aircraft Helps Quantum Technology Take Flight

1980s American aircraft helps quantum technology take flight

What does a 1980s experimental aircraft have to do with state-of-the art quantum technology? Lots, as shown by new research from the Quantum Control Laboratory at the University of Sydney, and published in Nature Physics today.

[caption id="attachment_452" align="aligncenter" width="695"]American Aircraft Helps Quantum Technology Take Flight American Aircraft Helps Quantum Technology Take Flight[/caption]

Over several years a team of scientists has taken inspiration from aerospace research and development programs to make unusually shaped experimental aircraft fly.

"It always amazed me that the X-29, an American airplane that was designed like a dart being thrown backwards, was able to fly. Achieving this, in 1984, came through major advances in a discipline called control engineering that were able to stabilise the airplane," said Associate Professor Michael Biercuk, from the School of Physics and director of the Quantum Control Laboratory.

"We became interested in how similar concepts could play a role in bringing quantum technologies to reality. If control engineering can turn an unstable dart into a high-performance fighter jet, it's pretty amazing to think what it can do for next-generation quantum technologies."

The result is that the researchers have been able to turn fragile quantum systems into useful pieces of advanced tech useful for everything from computation and communications to building specialised sensors for industry. The trick was figuring out how to protect them from their environments using control theory.

The big challenge facing quantum technologies is they are very sensitive to random 'noise' in surrounding environments, said Professor Biercuk. "Noise, in this case, is a bit like local electromagnetic weather experienced by a piece of hardware. Imagine your television only worked when the weather was perfectly sunny. Something needs to be done to make that technology more functional, even on the grey days."

The new field of quantum control engineering provided a path forward. The first step was trying to pinpoint how noise would affect a quantum system while it performed some task, which is fiendishly difficult.

"We were able to calculate how much damage is done to a quantum state using so-called transfer functions tailored to specific operations – for instance, manipulating a quantum system as a part of a computation," according to co-lead author, PhD student Harrison Ball.

The next issue was to show that the theoretical techniques actually worked.

"One of our main achievements has been to show – using experiments on real quantum systems in the form of atoms in a special trap – that the transfer functions were excellent at predicting how quantum systems changed in response to environmental noise."

With new capabilities to predict the effect of the environment on quantum systems, it became possible to protect them by applying the right control techniques.

"Similar to the control system that kept an aerodynamically unstable plane aloft, experiments revealed that our new techniques were able to keep the atoms performing useful computations," said Biercuk. "Turn off the new control techniques and they would crash and burn."

"Achieving this is a grand challenge for the entire community," according to Ball, and it is especially important as researchers move from proof-of-principle demonstrations to trying to develop real quantum technologies.

Working to make those technologies a reality is the aim of Prof. Biercuk and his colleagues in the ARC Centre for Engineered Quantum Systems.

"This may sound like futuristic fantasy, but the navigation system in your car works because of an early quantum technology – atomic clocks," according to Biercuk.

"We know that exotic phenomena like quantum systems being in two places at once, and even the ability to teleport quantum states, are real and accessible in the laboratory. Now we are trying to actually put them to work, and that means figuring out how to coax quantum systems into doing new and useful things."


Image Credit: NASA photo by Larry Sammons

News Release Source : 1980s American aircraft helps quantum technology take flight

Wednesday, October 15, 2014

Australian Teams Set New Records for Silicon Quantum Computing

Australian teams set new records for silicon quantum computing

UNSW Newsroom
13 October 2014

Two research teams working in the same laboratories at UNSW Australia have found distinct solutions to a critical challenge that has held back the realisation of super powerful quantum computers.

[caption id="attachment_445" align="aligncenter" width="500"]Australian Teams Set New Records for Silicon Quantum Computing Australian Teams Set New Records for Silicon Quantum Computing[/caption]

The teams created two types of quantum bits, or "qubits" – the building blocks for quantum computers – that each process quantum data with an accuracy above 99%. The two findings have been published simultaneously today in the journal Nature Nanotechnology.

"For quantum computing to become a reality we need to operate the bits with very low error rates," says Scientia Professor Andrew Dzurak, who is Director of the Australian National Fabrication Facility at UNSW, where the devices were made.

"We've now come up with two parallel pathways for building a quantum computer in silicon, each of which shows this super accuracy," adds Associate Professor Andrea Morello from UNSW's School of Electrical Engineering and Telecommunications.

The UNSW teams, which are also affiliated with the ARC Centre of Excellence for Quantum Computation & Communication Technology, were first in the world to demonstrate single-atom spin qubits in silicon, reported in Nature in 2012 and 2013.

Now the team led by Dzurak has discovered a way to create an "artificial atom" qubit with a device remarkably similar to the silicon transistors used in consumer electronics, known as MOSFETs. Post-doctoral researcher Menno Veldhorst, lead author on the paper reporting the artificial atom qubit, says, "It is really amazing that we can make such an accurate qubit using pretty much the same devices as we have in our laptops and phones".

Meanwhile, Morello's team has been pushing the "natural" phosphorus atom qubit to the extremes of performance. Dr Juha Muhonen, a post-doctoral researcher and lead author on the natural atom qubit paper, notes: "The phosphorus atom contains in fact two qubits: the electron, and the nucleus. With the nucleus in particular, we have achieved accuracy close to 99.99%. That means only one error for every 10,000 quantum operations."

Dzurak explains that, "even though methods to correct errors do exist, their effectiveness is only guaranteed if the errors occur less than 1% of the time. Our experiments are among the first in solid-state, and the first-ever in silicon, to fulfill this requirement."

The high-accuracy operations for both natural and artificial atom qubits is achieved by placing each inside a thin layer of specially purified silicon, containing only the silicon-28 isotope. This isotope is perfectly non-magnetic and, unlike those in naturally occurring silicon, does not disturb the quantum bit. The purified silicon was provided through collaboration with Professor Kohei Itoh from Keio University in Japan.

The next step for the researchers is to build pairs of highly accurate quantum bits. Large quantum computers are expected to consist of many thousands or millions of qubits and may integrate both natural and artificial atoms.

Morello's research team also established a world-record "coherence time" for a single quantum bit held in solid state. "Coherence time is a measure of how long you can preserve quantum information before it's lost," Morello says. The longer the coherence time, the easier it becomes to perform long sequences of operations, and therefore more complex calculations.

The team was able to store quantum information in a phosphorus nucleus for more than 30 seconds. "Half a minute is an eternity in the quantum world. Preserving a 'quantum superposition' for such a long time, and inside what is basically a modified version of a normal transistor, is something that almost nobody believed possible until today," Morello says.

"For our two groups to simultaneously obtain these dramatic results with two quite different systems is very special, in particular because we are really great mates," adds Dzurak.

The quantum bit devices were constructed at UNSW at the Australian National Fabrication Facility, with support from researchers at the University of Melbourne and the Australian National University. The research was funded by: the Australian Research Council, the US Army Research Office, the NSW Government, UNSW Australia and the University of Melbourne.
News Release Source : Australian teams set new records for silicon quantum computing
Image Credit : UNSW

Monday, October 6, 2014

Quantum computing will Create Smarter and Creative Robots

Pressing The Accelerator on Quantum Robotics

Quantum computing will allow for the creation of powerful computers, but also much smarter and more creative robots than conventional ones. This was the conclusion arrived at by researchers from the Complutense University of Madrid (UCM) and Austria, who have confirmed that quantum tools help robots learn and respond much faster to the stimuli around them.

[caption id="attachment_440" align="aligncenter" width="500"]Quantum computing will Create Smarter and Creative Robots Quantum computing will Create Smarter and Creative Robots[/caption]

SINC | October 02 2014 09:00

Quantum mechanics has revolutionised the world of communications and computers by introducing algorithms which are much quicker and more secure in transferring information. Now researchers from the Complutense University of Madrid (UCM) and the University of Innsbruck (Austria) have published a study in the journal ‘Physical Review X’ which states that these tools can be used to apply to robots, automatons and the other agents that use artificial intelligence (AI).

They demonstrate for the first time that quantum machines can respond the best and act the fastest against the environment surrounding them. More specifically, they adapt to situations where the conventional ones, which are much slower, cannot finish the learning and response processes.

“In the case of very demanding and ‘impatient’ environments, the outcome is that the quantum robot can adapt itself and survive, while the classic robot is destined to collapse,” explains G. Davide Paparo and Miguel A. Martín-Delgado, the two researchers from UCM who have participated in the study.

Their theoretical work has focused on using quantum computing to accelerate ahead with one of the most difficult points to resolve in information technology: machine learning, which is used to create highly accurate models and predictions. It is applied, for example, to know how the climate or an illness will evolve or in the development of Internet search engines.

More creative quantum robots

“Building a model is actually a creative act, but conventional computers are no good at it,” says Martín-Delgado. “That is where quantum computing comes into play. The advances it brings are not only quantitative in terms of greater speed, but also qualitative: adapting better to environments where the classic agent does not survive. This means that quantum robots are more creative”.

The authors assess the scope of their study as such: “It means a step forward towards the most ambitious objective of artificial intelligence: the creation of a robot that is intelligent and creative, and that is not designed for specific tasks”.

This work comes under a new discipline, the so-called ‘quantum AI’, an area in which the company Google has started to invest millions of dollars via the creation of a specialised laboratory in collaboration with the NASA.

Referencia bibliográfica:

Giuseppe Davide Paparo, Vedran Dunjko, Adi Makmal, Miguel Angel Martin-Delgado, and Hans J. Briegel. “Quantum Speedup for Active Learning Agents”. Phys. Rev. X 4, 031002, 8 de julio de 2014.

News Release Source : Pressing the accelerator on quantum robotics

Image Credit : SINC

Sunday, October 5, 2014

Quantum environmentalism

Quantum environmentalism

Putting a qubit's surroundings to good use

Where are the quantum computers? Aren't they supposed to be speeding up decryption and internet searches? After two decades of research, you still can't find them in stores. Well, it took two decades or more of research dedicated to semiconductors and circuit integration before we had digital computers. For quantum computers too it will take technology more time to catch up to the science

[caption id="attachment_436" align="aligncenter" width="512" class=" "]Quantum environmentalism The electron spin (black arrow) inside a quantum dot interacts magnetically with the effective magnetic field (orange arrow) of the nuclei of the atoms forming the atomic environment of the electron.[/caption]

Meanwhile, research devoted to exploring bizarre quantum phenomena must continue to overcome or reduce a litany of practical obstacles before quantum computing can be realized. Not the least of these obstacles remains the isolation of qubits---the repository of quantum information---from their surroundings. A qubit, or better yet an ensemble of qubits, exists in a superposition of two or more possible states. The trouble is that superposition is a fragile condition, and the manipulation and final readout of those states are in danger of being undone if a qubit interacts with its environment. A new paper, published in Nature Physics (1) addresses this problem by demonstrating a new type of qubit control, one that actually makes productive use of a qubit's proximity to its surroundings.

The experimental work was performed at the Cavendish Laboratory at Cambridge University in the UK. JQI (2) scientist Jacob Taylor provided the theoretical input to the work over the course of five years of cross-Atlantic collaboration.

ENVIRONMENTAL-ASSISTED CONTROL Qubits come in many forms but have one essential thing in common: they all embody a physical system---whether in the form of a photon or atom or electron or electrical current---which exists in two quantum states simultaneously. In the Cambridge experiment the qubit is a single electron trapped in a semiconductor. The two quantum states, in this case, consist of the two orientations for the electron's tiny spin, either up or down.

The electron's trap is a tiny region of the semiconductor called a quantum dot, essentially a zero-dimensional volume housing a single active electron. When studied at a temperature of about 4 K, the electron spreads as a wave across the 10 nanometer length of the quantum dot. The dot can be considered to be an artificial atom in which the electron (instead of orbiting a single nucleus) is confined in the crystalline lattice of millions of atoms. And like electrons in regular atoms, the select electron in a quantum dot possesses an energy spectrum of discrete energies.

The dot is fabricated using existing nanotechology. In substance it is a tiny lump of indium arsenide (InAs) grown amidst surrounding thicker layers of gallium arsenide (GaAs). Recall the story of the princess and the pea; a girl confirms her status as a princess by detecting a very faint lumpiness created by the presence of a single pea sandwiched between much larger mattresses.

Here the pea is the InAs quantum dot and the mattresses are the GaAs layers. The two species of semiconductor blend, InAs and GaAs, are incommensurate, meaning that their natural atomic spacings are slightly different. In practice this ensures that the atoms in the InAs dot are under some stress amid the surrounding GaAs atom layers. This stress, in turn, leads to the growth of such small 'pea'-like dots, confining the electron inside. Fortunately, one can probe the properties of these buried quantum dots via light, as the materials are transparent, allowing experimentalists to control and manipulate the electron using lasers.

The electron's energy spectrum is made still more complicated by the faint magnetic interaction between it and the nuclei of all those indium and arsenic atoms. Each of those nuclei has a net magnetic field and behaves as if it were a tiny magnet. Those nuclei, in the absence of an external magnetic field, are pointing in all different directions. But at any one moment, the totality of the nuclei exert a single, effective field, which the electron senses. The collective nuclei form a magnetic "environment" for the electron. In just a moment we'll see how the electron is employed as a qubit and how its environment---usually viewed as a threat to maintaining the quantum integrity of the qubit---is actually put to use in the process of manipulating and reading out the qubit.

QUANTUM DARK STATES If a laser strikes the quantum dot at certain wavelengths corresponding to allowed electron energies, the dot will absorb and then reemit light. It will fluoresce. Things get more interesting, however, if the electron can be coaxed into not absorbing light. To do this a dark state must be created. Generally, if a laser beam is tuned to the energy difference between two quantum levels, the atom can absorb laser light and be promoted to the more excited of the two states. The continued presence of the laser light will later stimulate the atom to re-emit the light and return to its lower (ground) state. In some circumstances this absorption/emission process can be stymied if there are closely spaced ground states.

Two laser beams, one tuned to promote the atom from state 1 to state 3 and one tuned to promote the atom from state 2 to state 3, can interfere with each other, leaving state 3 unreachable. This destructive interference can be turned on and off by changing the relative phase of the two laser beams.

This method is employed in the Cambridge experiment. The quantum dot qubit consists of the lone electron being maintained in a state of superposition (spin up and spin down) by laser light. Moreover, the presence of the underlying nuclear magnetic field forming the electron's "environment" helps establish a two-part ground state. Thereafter, the combination of the environment, plus the presence of two carefully-tuned laser beams allows the state of the qubit to be controlled (swiveled around in space) and even to be read out when detectors glimpse the electron as a bright (fluorescent) or a dark object.

In quantum computing, the explicit state of the qubit is unknown (spin up or spin down); this is positively a necessary condition---a required indeterminacy---for the quantum computation to continue. The only thing required is that one knows the relative change in the qubit, such as whether it was swiveled through an angle of 90 or 180 degrees. In conventional computing an example would be a NOT gate, which changes a bit from a 1 state into a 0 state or vice versa. It's only important to know the relative change in the bit, not its actual value. "What is profound is that the electron spin is always in the same quantum superposition, but the physical state evolves with the nuclear field," notes Mete Atature, the Cambridge researcher leading the experimental study.

"Usually you need an external magnetic field to manipulate qubits," says Jacob Taylor, "but this single field can't be used also to read out the final state of a qubit. In our all-optical approach we don't use a field so we can perform manipulation and readout with a single setup."


1. "Environment-assisted quantum control of a solid-state spin via coherent dark states," Jack Hansom, Carsten H. H. Schulte, Claire Le Gall, Clemens Matthiesen, Edmund Clarke, Maxime Hugues, Jacob M. Taylor, Mete Atatüre, Nature Physics, Nature Physics 10, 725–730 (2014), doi:10.1038/nphys3077; published online 7 September 2014

2. The Joint Quantum Institute (JQI) is operated by the National Institute for Standards and Technology and the University of Maryland (

3. Previous press release about 3-electron quantum dot qubits:

4. Previous press release about reducing noise in quantum-dot qubits:

5. Previous press release about Bloch spheres and how to manipulate qubits:

Jacob Taylor,

Press contact at JQI: Phillip F. Schewe,, 301-405-0989.


News Release Source :  Quantum environmentalism