Physicists Transcribe Entanglement into and out of a Quantum Memory
March 6, 2008Scientists at the California Institute of Technology have laid the groundwork for a crucial step in quantum information science. They show how entanglement, an essential property of quantum mechanics, can be generated between beams of light, stored in a quantum memory, and mapped back into light with the push of a button.
In the March 6 issue of the journal Nature, Caltech Valentine Professor of Physics H. Jeff Kimble and his colleagues demonstrate for the first time an important capability required for the control of quantum information and quantum networks, namely the coherent conversion of photonic entanglement into and out of separated quantum memories.
Entanglement lies at the heart of quantum physics, and is a state where parts of a composite system are more strongly correlated than is possible for any classical counterparts regardless of the distance separating them. Entanglement is a critical resource for diverse applications in quantum information science, such as for quantum metrology, computation, and communication. Quantum networks rely on entanglement for the teleportation of quantum states from place to place.
In a quest to turn these abstract ideas into real laboratory systems and to distribute entanglement to remote locations (even on a continental scale), Kimble explains that quantum physicists have studied ways to propagate photonic information into and out of quantum memory using a system called a quantum repeater, invented in 1998 by H. Briegel, J.I. Cirac, and P. Zoller at the University of Innsbruck. Until now, work in Kimble's group on the realization of a quantum repeater with atomic ensembles relied upon the probabilistic creation of entanglement. In this setting entanglement between two clouds of atoms was generated probabilistically but with an unambiguous heralding event.
While such systems hold the potential for scalable quantum networks, it has been difficult for Kimble's Quantum Optics Group to apply such schemes to certain protocols necessary for quantum networks, such as entanglement connection. Now, with the new protocol and future improvements, "We can push a button and generate entanglement," says physics graduate student Kyung Soo Choi, one of four authors of the Caltech experiment.
While entanglement has been traditionally carried out with photons in attempt to connect two distant systems, these particles of light are difficult to store because of their small interactions with matter when taken one by one. A quantum memory for light is an essential ingredient for achieving scalable quantum networks with photons. Choi says. "The question is now, 'How do you change the entangled state of light into an entanglement of matter and back into light?'" This was not possible for any physical system until now.
The new work, Choi says, "is a proof-of-principle demonstration that entanglement between material systems can be generated deterministically by mapping the entanglement of light to and from two spatially separated quantum memories." The Caltech team separated the processes for generating and storing the entanglement, thereby breaking a previous inherent link between the quality and probability of state preparation. "In a general context, our work represents an important step in laboratory capabilities for the creation and manipulation of entangled states of light and matter. We hope that our results will be useful as a tool in the effort to realize quantum repeaters and thereby scalable quantum networks over long distances," remarks Kimble.
In the Caltech experiment, a single photon is first split, generating an entangled state of light with quantum amplitudes for the photon to propagate two distinct paths, taking both at once. The Caltech team in turn transcribed, or mapped, the entanglement onto distinct atomic ensembles separated by one millimeter. To create the interface between the light and matter, the team employed laser-cooled cesium atoms whose atomic states interact with a control laser to create destructive quantum interference, making the atomic ensembles either invisible or highly opaque to the input light. Called Electromagnetically Induced Transparency and pioneered by S. Harris at Stanford University, the mechanism manipulates the speed of the light for the incoming entangled photon and that kicks off the entire procedure.
"We can reduce the speed of light to the speed of a train, and then in fact stop the light inside the matter by slowly turning off the control laser, where now the quantum information--the entangled state of light--is stored inside the atomic ensembles," Choi describes. "By turning on the control laser again, we can reversibly accelerate the 'stopped' light back to the speed of light and restore the quantum entanglement as propagating beams of light."
In this experiment, the photonic entanglement was mapped into the atomic ensembles in a time ~ 20 nanoseconds and then stored in the atomic ensembles for one microsecond, with storage times extendable up to 10 microseconds. The photonic entanglements of the input and output of the quantum interface were explicitly quantified with a conversion efficiency of 20 percent. However, the researchers emphasize, real-world realization of a quantum network remains far out of reach even with these parameters and the state-of-the-art of quantum controls. Choi comments, "Further improvements in quantum control and storage capabilities in matter-light interfaces will lead to fruitful and exciting discoveries in Quantum Information Science, including for the realization of quantum networks."
Source: Caltech
-
Quantum physicists shed new light on relation between entanglement and nonlocality
Jan 30, 2012 |
4.6 / 5 (24) |
35
-
Speed limit on the quantum highway
Jan 26, 2012 |
4.9 / 5 (15) |
0
-
JQI cool nano loudspeakers could makes for better MRIs, quantum computers
Jan 25, 2012 |
4.8 / 5 (4) |
0
-
Physicists cool semiconductor by laser light
Jan 22, 2012 |
4.5 / 5 (11) |
2
-
Quantum mechanics enables perfectly secure cloud computing
Jan 19, 2012 |
4.2 / 5 (15) |
13
-
Engineers build first sub-10-nm carbon nanotube transistor
Feb 01, 2012 |
4.9 / 5 (31) |
30
-
Something old, something new: Evolution and the structural divergence of duplicate genes
Jan 31, 2012 |
4.6 / 5 (7) |
1
-
The hidden nanoworld of ice crystals: Revealing the dynamic behavior of quasi-liquid layers
Jan 30, 2012 |
5 / 5 (3) |
1
-
Stock market network reveals investor clustering
Jan 27, 2012 |
3.9 / 5 (23) |
8
-
Of microchemistry and molecules: Electronic microfluidic device synthesizes biocompatible probes
Jan 26, 2012 |
5 / 5 (1) |
0
-
Rust from my microwave ruined a nice bowl of soup and also my day
2 hours ago
-
gas leaks in space
6 hours ago
-
Weight required to balance a boom stand?
7 hours ago
-
Questions about Equivalence principle & Einstein Elevator?
9 hours ago
-
Kinetic energy of gas
10 hours ago
-
Understanding induced emfs
12 hours ago
- More from Physics Forums - General Physics
More news stories
Explained: Sigma
It's a question that arises with virtually every major new finding in science or medicine: What makes a result reliable enough to be taken seriously? The answer has to do with statistical significance -- but ...
Feb 09, 2012 |
5 / 5 (19) |
72
Quantum physicist explains $100K offer for proof scaled-up quantum computing is impossible
(PhysOrg.com) -- MIT researcher Scott Aaronson has certainly riled the physics community with his offer this past Friday, of $100,000 to anyone who can prove that scaled-up quantum computing is impossible. ...
Diamond light, brighter than the sun
Its the size of five football pitches and generates light 10 billion times brighter than the sun. As the Diamond Light Source celebrates its tenth anniversary this year, Penny Bailey visits one of the ...
Feb 07, 2012 |
4.3 / 5 (7) |
18
|
Physicists 'record' magnetic breakthrough
An international team of scientists has demonstrated a revolutionary new way of magnetic recording which will allow information to be processed hundreds of times faster than by current hard drive technology.
Feb 07, 2012 |
4.5 / 5 (41) |
14
|
Hints of the Higgs - papers are submitted
Back in December 2011, the ATLAS and CMS experiments at CERN presented some exciting results that provided tantalising hints of the Higgs boson.
Feb 08, 2012 |
4.1 / 5 (7) |
10
Google might launch Drive for cloud storage soon
(PhysOrg.com) -- Google's next big move, according to the Wall Street Journal, is a cloud storage service called Drive. Hardly first to the plate, Google is simply catching up to introducing its cloud reposi ...
Latin America mining boom clashes with conservation
Latin America is experiencing a mining boom as prices rise fuelled by a hike in global demand, but the region is also being hit by a wave of violent protests, strikes and rallies by environmentalists.
Walney offshore wind farm is world's biggest (for now)
(PhysOrg.com) -- The Walney wind farm on the Irish Sea--characterized by high tides, waves and windy weather--officially opened this week. The farm is treated in the press as a very big deal as the Walney ...
Love a click away in Indonesia's Twitter Republic
He was a geeky kid from Yogyakarta, she a glamorous city girl in Jakarta. In a country with one of the world's most vibrant social networking scenes they fell in love on Twitter.
GPS court ruling leaves US phone tracking unclear
A US Supreme Court decision requiring a warrant to place a GPS device on the car of a criminal suspect leaves unresolved the bigger issue of police tracking using mobile phones, legal experts say.
Europeans protest controversial Internet pact
Tens of thousands of people marched in protests in more than a dozen European cities Saturday against a controversial anti-online piracy pact that critics say could curtail Internet freedom.
Mar 06, 2008
Rank: 1 / 5 (1)
Mar 06, 2008
Rank: 1.7 / 5 (3)
Mar 07, 2008
Rank: 3 / 5 (2)
So, whenever you'll split such undulating droplet into two halves by wire, the resulting parts will remain undulate at phase with respect to the center of their common mass. The resulting smaller dropplets will therefore remember the state of the original droplet in certain extent, so they can serve as a quantum memory. Such pair will create their own "local universe" by Everett interpretation. because it's members are "entangled" at the distance - and as you can see, nothing "spooky" is on such entaglement, in fact.
Note that even though you can combine the different droplet pairs with the same surface amplitude or even frequency, such reconnection will not restore the original surface wave, until the phase of the surface waves will not remain exactly the same - from this the quantum cryptography follows.