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DIAMONDS ARE FOREVER: Qubits in diamond may not last forever, but they do last a long time by quantum-physics standards. Physicists have figured out a way to encode quantum information onto a single carbon atom in a synthetic diamond for more than one second. (The diamond pictured above is for illustration purposes only.)
Image: © Roydee/iStockphoto
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BOSTON—The quantum world and the everyday world of human experience are supposed to be two different realms. Quantum effects, as demonstrated in the lab, are usually confined to the tiniest scales. They last for imperceptibly brief instants. And they appear mostly in highly controlled systems operating at cryogenic temperatures near absolute zero.
But experimental physicists are pushing across the assumed divide between the quantum and the ordinary by demonstrating quantum effects in more familiar environments. Now a group of researchers has furthered that cause by encoding quantum information into a room-temperature solid for time spans that can be ticked off on a stopwatch. The new quantum memory scheme can store information for more than a second, which extends by orders of magnitude the lifetime of information encoded as a quantum bit, or qubit, on a particle at ordinary temperatures. The American, German and British researchers have only just submitted the research to a peer-reviewed journal, but here in late February they presented their findings to a meeting of the American Physical Society.
A qubit, much like an ordinary bit in commonplace electronic devices, has a 0 state and a 1 state. But unlike a classical bit, a qubit can be in a so-called superposition of 0 and 1. That property, along with other phenomena such as quantum entanglement, means that quantum computers based on qubits would be phenomenally powerful—that is, if a practical machine could ever be built.
But that power comes at a price. A qubit can easily be corrupted by outside influences such as heat and magnetic fields. Physicists have produced long-lived qubits by all but eliminating such noise, confining individual atoms to vacuum traps or cooling them nearly to absolute zero. But some research groups have been trying to design qubits that can operate in solid-state systems at room temperature—to make a qubit, in short, that can survive in the world of the bit.
In the latest advance on that front, the research groups of Mikhail Lukin of Harvard University and Ignacio Cirac of the Max Planck Institute of Quantum Optics in Garching, Germany, and their colleagues encoded long-lived quantum information in the spin of a single-atom impurity in a synthetically produced diamond. Spin is a quantum property akin to the pointing of a particle's internal bar magnet, either up or down, representing 1 or 0.
The experimental quantum-grade diamond is 99.99 percent pure carbon 12, the most common isotope of the element. But the crystal also contains a small amount of the heavier isotope carbon 13 as well as implanted nitrogen ions that form defects in the diamond lattice known as nitrogen vacancy centers. Both impurities have certain quantum benefits.
Each, for example, features an intrinsic spin with a special talent. The nitrogen ion has an associated electron whose spin state is readily detectable by shining laser light on the nitrogen vacancy center. The carbon 13's nuclear spin state remains stable for long intervals.
The researchers figured out a way to combine these two attributes. Their approach uses the carbon 13 to store information for long periods of time and the nitrogen ion as a readout.
The scientists located an area in the diamond where a carbon 13 and a nitrogen ion are only about two nanometers apart. At that distance the spin of the nitrogen ion's electron and that of the nearby carbon nucleus couple together—the electron acts as a tiny magnetometer that reflects the carbon 13's nuclear spin state. By hitting the nitrogen vacancy center with laser light, the researchers can measure the electron's spin and, by extension, the spin of the carbon 13 nucleus.
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12 Comments
Add CommentPerhaps I'm just old-fashioned, but I don't really understand how a bit containing the superposition of 0 and 1 states could serve the requirements for deterministic information processing. How can uncertain information be usefully processed?
Reply | Report Abuse | Link to thisMoreover, these experiments produce a single qubit by identifying a special "area in the diamond where a carbon 13 and a nitrogen ion are only about two nanometers apart," coupling their spin states so they can be determined. These methods seem to be far removed from the production of any potential reliable high capacity storage device...
Good questions. As far as I've been able to follow it (which isn't very far really) the attraction is that by defining on particles identity on a quantum basis, the linked particle is immediately defined as well, thereby creating a means of transmission or cummunication of data.
Reply | Report Abuse | Link to thisIn doing this the speed limits within a circuit (ie., the speed of light) are eliminated thereby allowing massively faster computing times and massively smaller computers.
That they are able to demonstrate control of quantum materials at microscopic scales is amazing.
I don't believe it's about speed of computation or size of the computer, no. As far as I understand it, it's about the potential efficiency of the calculations. Having a bit that can exist in two states at once essentially allows it to function as a variable (x, y, etc.). As I understand it, traditional computers can handle variables only as unknowns that must be solved for one at a time, whereas quantum computers can handle multiple variables in a way that the collapse of the wave form produces a solution that takes all the variables into account, without solving them in a linear or sequential fashion. Whether this description captures it well or not, it is certainly true that calculations in qubits reduces the number of calculations needed for certain problems dramatically, with the result that certain intractable problems become easily solvable. Such problems include the factoring of large numbers whose factors consist only of large primes, and the traditional travelling salesmen problem and its equivalents. Today, such calculations are doable in theory, but not in practice (some would take longer than the age of the universe). So mathematically, quantum computation (if they can get it working) is a very, very big deal, not just a curiosity.
Reply | Report Abuse | Link to thisYou may be on to something, but wouldn't each retrieval of variable x at storage location s collapse its value to some specific state, 0 or 1 (or something in between)? In that case I don't see any opportunity for parallel array processing, only for randomized data...
Reply | Report Abuse | Link to thisI am in awe of this research. It is articles like this that make SA so well worth reading.
Reply | Report Abuse | Link to thisAs I understand it, while each retrieval would collapse its value... the retrieval wouldn't take place until all the necessary qubits have been put into their required state. This then sets up the desired "formula" - and retrieving the data forces the solution of the equation. In order to do this, it is necessary to have enough qubits available for a long enough period of time to get things going. This is merely the first step in achieving that initial goal.
Reply | Report Abuse | Link to thisThanks, but I think that there are many fundamental disconnects between the terminology used to describe quantum computer theory and what quantum computer theorists refer to as "classical" computing.
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Quantum_algorithm states:
"All problems which can be solved on a quantum computer can be solved on a classical computer. In particular, problems which are undecidable using classical computers remain undecidable using quantum computers. What makes quantum algorithms interesting is that they might be able to solve some problems faster than classical algorithms."
The wikipedia entry goes on to discuss several computationally intense functions that are usually included in supercomputer architectures but not necessarily in general purpose computing architectures, including a section on "Algorithms based on the quantum Fourier transform".
I suspect that the types of computations that might be processed more quickly on quantum computers are those that can process large arrays of data in parallel using a single instruction stream, like supercomputers. These methods often offer no benefit for problems that must be computed serially.
I still don't really understand how qubits fit into the computing architecture, but this is quite enough for this old guy. I may not be around when this research produces any useful computers.
Thanks for all the help!
Thanks for the explanantion. Very cool stuff.
Reply | Report Abuse | Link to thisJust to clarify, you did begin your comment by stating: "I don't believe it's about speed of computation," and concluding it with "Today, such calculations are doable in theory, but not in practice (some would take longer than the age of the universe)."
Reply | Report Abuse | Link to thisThe class of computers known as 'supercomputers' applies fundamentally similar methods to very complex problems that require the application of a computational processes to a very large number of variable values. Most modern supercomputers achieve this by cost effectively employing many individual standard processors in parallel to a single instruction execution concurrently applied to very large arrays of variables.
As I understand, these same basic parallel or array processing methods are intended in quantum computing models to concurrently apply a single calculation to a very large number of variable values, somehow facilitated by the probabilistic values of qubits. Please refer to the wikipedia entry I referenced in my preceding comment. Also please see: http://en.wikipedia.org/wiki/Quantum_computer
especially the section:
http://en.wikipedia.org/wiki/Quantum_computer#Relation_to_computational_complexity_theory
That depends on the application. Would indeterminate billing for electric service be 'good enough'?
Reply | Report Abuse | Link to thisMy employer recently gave that a shot but it didn't go over well with our customers or board of directors.
Reply | Report Abuse | Link to thisCan the fast flip-flop state be used as a QBIT. That is can the state of the overall crystal's electrons be placed either up or down then the state of the qbit could be set by simply turning on the light? Would this make a simpler micro-chip with a light pipe? Or is this state too unstable?
Reply | Report Abuse | Link to thisWhat I'm getting at is, if the stability is changed, how different is the stability of the electron we are trying to set and the overall crystal? How long would this delta exist? Is it detectable?
Rufus