The idea of a quantum computer was first proposed by Richard Feynman in 1981 as a way to solve intractable quantum mechanical problems[1].  Since then, quantum computers were proven to be inherently superior at solving certain problem than their classical counterparts[2,3].  In addition, communication across quantum channels offers absolute security because it is impossible to eavesdrop on a transmission without disturbing it [4,5] To date, quantum computers have solved only trivial problems, and secure communication is limited to about 200 km [6].  Continued progress in computing and signal amplification in communication will require scalable systems that can perform basic quantum information processing functions.  We have recently developed a technique to coherently probe an atomic system -- a semiconductor quantum dot -- that is strongly coupled to a photonic crystal nanocavity.  The article is published in Nature[7]. 

Nature:  Controlling Cavity Reflectivity With a Single Quantum Dot, Dirk Englund, Andrei Faraon, Ilya Fushman, Nick Stoltz, Pierre Petroff, Jelena Vuckovic, Nature, vol. 450, number 7171, pp. 857-861 (2007)

- Stanford researchers develop a quantum "light switch" Stanford Report story (Dec. 7, 2007)

- Optics.org: Two teams unveil quantum-dot light switch (Dec. 7, 2007)

- Nanotechnology Now (Dec. 11, 2007) 

- Pro-Physik (in German) (Dec. 12)  

- Office of Naval Research - news

 -On Cvitae: Dirk Englund, Andrei Faraon, Ilya Fushman, Jelena Vuckovic
 

Q: What's the goal of your research?

Whether classical or quantum mechanical, information is ultimately stored in some physical system -- for example, on your hard drive it's stored in local magnetization.  The magnetization is stored across a large number of atoms, and the ensemble behaves classically, rather like larger magnets that we know from our macroscopic world.  However, if the information is stored and manipulated in things that behave quantum mechanically (like the magnetization of a single atom), then a much more powerful computer could be constructed. Such a quantum computer could simulate intractable problems in nature (like protein folding in biology or drug discovery), or it could be used to decrypt classical encoding (which makes it interesting for national security or policing).  It is also possible to build long-range communication systems that are unconditionally secure (even against a quantum computer). This is called quantum cryptography.

Q: Why are QED systems an important area of research?

Several approaches exist for implementing quantum information systems. One would like to use photons, which are great for carrying quantum information. But they do not interact, so it's difficult to use them for logic gates.  Atomic systems are much better at interacting, but are bad for communication.  So one way that people hope to achieve quantum computers and long-distance quantum cryptography is to combine the best of both worlds through something called a quantum network.  This network combines atomic nodes that are connected through photonic quantum bits (qubits).  The interface between photons and emitters is governed by quantum electrodynamics.  Our group pursues this approach. 

One of the major difficulties in the network approach is transferring the quantum information from the atom-like particle (a quantum dot in our case) to the photon.  We place the quantum dot inside cavities, which recirculates the photon so that it has a much longer interaction time with the quantum dot.  Our photonic crystal system allows cavities with extremely low loss and small volume, so the photon is kept extremely close to the quantum dot for a long time, and can thus interact efficiently with it.