The catch is that the electron's spin is not as stable as the nuclear spin of the carbon atom; it fluctuates on the millisecond timescale. And once the electron changes its spin, the information in the qubit is lost. "A single electronic spin flip completely destroys the coherence of our nucleus," said Georg Kucsko, a member of Lukin's research group who presented at the meeting. To keep the electron's flip-flopping from affecting the nucleus, the researchers continually reset the electron's spin with green laser light, essentially turning off the interaction between electron and nucleus when that interaction is not needed.
"In order to make things better, you make it worse," says solid-state quantum physicist Fedor Jelezko of the University of Ulm in Germany, who was not part of the new research. "If the electron flips very fast, the nucleus will not see it anymore. It creates some average field that does not fluctuate."
Using that tactic, along with a sequence of radio-frequency pulses to suppress interactions with other carbon nuclei in the diamond, the researchers were able to store quantum information at ambient temperatures for nearly two seconds. That is a significant leap from previous experiments, where storage times in single qubits have generally been measured in microseconds. "There were really no examples before of such long coherence times, except perhaps in trapped atoms or ions," Jelezko says. And the vacuum traps and laser-cooling apparatuses required for those laboratory setups would be prohibitively complex for some applications.
"The demonstration of a single-qubit quantum memory with seconds of storage time at room temperature is certainly exciting," adds Nick Vamivakas, an optical physicist at the University of Rochester who was not part of the research team. "I am not aware of another system that is being investigated for quantum information purposes that has demonstrated memory lifetimes on the second timescale."
Kucsko added that even better storage times ought to be attainable by stabilizing the diamond's temperature to eliminate thermal drifts that limit the qubit's life span. Purifying the diamond even further, thereby reducing the number of secondary carbon 13 impurities that can interact with the qubit, would also help. Lukin noted that with such improvements, storage times measured in hours might even be possible. "We have really an excellent qubit at room temperature which combines memory, control and measurement—all three things," he said. "We're actually quite excited about this new development."
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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