Scientists Extend the Lifetime of Quantum Memory

Jan 02, 2009 By Laura Mgrdichian feature

(PhysOrg.com) -- Storing and sending information using quantum phenomena is one of the hottest areas of research today; scientists across the globe are investigating how to make quantum communication possible for real-life applications. In a key step, a group of researchers was recently able to greatly improve the lifetime of a form of quantum memory.

In this case the research group achieved a quantum memory lifetime of 6 ms, more than 100 times as long as the next-best reported time. The scientists—from the Georgia Institute of Technology, the University of Maryland, and Università degli Studi dell’Insubria (Unviersity of Insubria), in Italy—describe their work in the December 7 online edition of Nature Physics.

“Though several technical hurdles still remain, this advance represents a significant step toward the realization of quantum networks and the distribution of entangled states over long distances,” said corresponding author Stewart Jenkins to PhysOrg.com. Jenkins is affiliated with both Georgia Tech and the University of Insubria.

Quantum memory schemes are extremely sensitive to the surrounding environment, limiting how long they can store data. To transmit quantum information over a long distance, the storage times must be longer than scientists have been able to achieve thus far. Transmitting quantum information across 1,000 kilometers, for example, takes a minimum of 5 milliseconds (ms), meaning that a quantum-memory scheme must be viable for at least that long.

This group's work takes advantage of rubidium's "clock transition," the movement of electrons between two specific energy levels. This electron jump is what makes rubidium atoms appropriate for use in atomic clocks, in which the standard for keeping time is based on the precise (and unchanging) frequency of microwaves emitted when the electrons undergo the transition.

The transition is the medium by which the atoms store quantum information. The process involves three key atomic energy levels, denoted a, b, and c, where a is the lowest and c is the highest. The energy difference between a and b is very small; they are "hyperfine" levels of the ground state, the lowest state of an atom.

Jenkins and his colleagues trapped between 100,000 and one million super-chilled rubidium atoms within a lattice of laser beams, which separated and immobilized the atoms into a grid-like pattern. They then "set" the atoms to the proper excitation state using a "write" laser, imparting the atom's electrons with enough energy to move from b up to c. The transition represents a value of one bit, the most basic unit of information, typically denoted as a "0" or "1." (In conventional memory schemes, bits are often defined by capacitors, with a charged capacitor representing a "1" and an uncharged capacitor representing a "0.")

The electrons quickly decayed from the c level, but jumped down to a rather than back to b. This is due to energy loss from the light they emitted during the jump, know as Raman radiation.

Finally a "read" laser was applied to the atom array, exciting the a-to-c transition. The electrons decayed from c to b, emitting a second, weaker round of Raman emission, known as the "idler" field. The idler field is detected and interpreted, allowing the researchers to "read off" the information that had been briefly stored.

This approach differs from previous rubidium quantum-memory schemes. The longest memory time prior to this work was achieved using a free-moving, magnetically sensitive rubidium-atom ensemble; it had a lifetime of 32 microseconds. But the atoms were able to fall freely, which, in conjunction with small magnetic fields, resulted in a limited memory time.

In this case, the atoms' motion is greatly suppressed and the clock transition is not sensitive to magnetism. These features greatly improve the memory time.

Quantum communication is based on the phenomenon of entanglement, the mysterious way in which two quantum entities, such as photons (light particles), can "know" each other's quantum state despite never having been in contact. Parties in remote locations share and store the entangled state, thus transmitting a quantum bit across a distance.

More information: Nature advance online publication, 7 December 2008 DOI: 10.1038/nphys1152

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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User comments : 12

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superhuman
1 / 5 (2) Jan 04, 2009
Id like to propose a hypothetical general rule of quantum computing:

The less common the entities capable of absorbing the state transition energy are in the Universe the longer it will survive before decaying.
Velanarris
3.7 / 5 (3) Jan 05, 2009
Id like to propose a hypothetical general rule of quantum computing:

The less common the entities capable of absorbing the state transition energy are in the Universe the longer it will survive before decaying.

So entities created by man that decay in nanoseconds should be able to hold data an exponential amount of time longer than it takes to decay...


Hypothesis verified as false through logic.
superhuman
1 / 5 (2) Jan 06, 2009
V as usual you fail to understand the things you are talking about.

Entities produced by humans are made of atoms which are abundant everywhere with energy states whose energy is readily absorbed, for quantum states to last long exotic energy levels have to be utilized, levels whose decay energy cannot be absorbed by normal matter.

I don't expect you will understand, I've seen enough of your ignorant statements to know you have no idea about physics at all, I only explain it in case someone else might be confused by your misguided comment.
Velanarris
3 / 5 (2) Jan 06, 2009
V as usual you fail to understand the things you are talking about.

Entities produced by humans are made of atoms which are abundant everywhere with energy states whose energy is readily absorbed, for quantum states to last long exotic energy levels have to be utilized, levels whose decay energy cannot be absorbed by normal matter.
Sorry SH that's incorrect. We've "made" several sub atomic particles by using exotic energies in the relativistic colliders. None of which have stuck around long enough for quantum storage testing.

I don't expect you will understand, I've seen enough of your ignorant statements to know you have no idea about physics at all, I only explain it in case someone else might be confused by your misguided comment.
And with comments like the preceding I'm pretty sure they're not going to assume you're very knowledgable about the subject as you've brought nothing of value to the table.
superhuman
1 / 5 (2) Jan 07, 2009
Sorry SH that's incorrect. We've "made" several sub atomic particles by using exotic energies in the relativistic colliders. None of which have stuck around long enough for quantum storage testing.

See, you already managed to contradict yourself. If they don't last they are obviously irrelevant to my hypothesis.
Velanarris
3 / 5 (2) Jan 07, 2009

See, you already managed to contradict yourself. If they don't last they are obviously irrelevant to my hypothesis.


"The less common the entities capable of absorbing the state transition energy are in the Universe the longer it will survive before decaying."

Where's the contradiction? Your lack of clarity and accuracy in your hypothesis is the issue, not my statements pointing out your lack of clarity and accuracy.
superhuman
1 / 5 (2) Jan 07, 2009
I have neither time nor will to educate you.
Velanarris
3 / 5 (2) Jan 07, 2009
I have neither time nor will to educate you.


Quite alright. The feeling and situation are mutual.
moj85
5 / 5 (2) Jan 07, 2009
wow. *claps*
Velanarris
3 / 5 (2) Jan 07, 2009
I have neither time nor will to educate you.



And by the way
for quantum states to last long exotic energy levels have to be utilized, levels whose decay energy cannot be absorbed by normal matter.


Negative energy? Give me a break.
Going
not rated yet Jan 09, 2009
I for one welcome our new quantum computer overlords.
zevkirsh
not rated yet Jan 13, 2009
I PROPOSE A THEORY. quantum electronics will yield a huge discovery that has absolutley nothing to do with electronics and computing. and will much more relevant to power generally. perhaps yielding a new way of moving heat in an organized pattern, or preserving and manipulating magnetic fields, which will yield room temperature superconducting, if not something MUCH more interesting.

conventional computing reserach with silicon ( and possibly advance materials such as graphene ) is and will continute to dominate the supercomputing field and computing generally, as software, hardware, and cloudware ( networking hardware ) continue to revolutionize the boundaries of super computing, conventional computing and network computing.

quantum computing will yield miracles. just not in computing.

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