Quantum Information Technology: Entanglement, Teleportation and Quantum Memory

Quantum superposition and quantum entanglement are the bedrock on which new theoretical paradigms for information transmission, storage, and processing are being built. The preeminent obstacle to the development of quantum information technology is the difficulty of transmitting quantum information over noisy and lossy quantum communication channels, recovering and refreshing the quantum information that is received, and then storing it in a reliable quantum memory.

With support from the Multidisciplinary Research Program of the University Research Initiative (MURI), we have assembled an interdisciplinary team from researchers at MIT and Northwestern University to overcome this obstacle. The focus of our program is an architecture we have established for long-distance, high-fidelity qubit teleportation. Its key elements are: (1) ultrabright, narrowband sources of polarization-entangled photon pairs; (2) long-distance transmission of entangled photons over standard telecom fiber; and (3) qubit storage and processing in trapped atom quantum memories.

The preeminent obstacle to the development of quantum information technology is the difficulty of transmitting quantum information over noisy and lossy quantum communication channels, recovering and refreshing the quantum information that is received, and then storing it in a reliable quantum memory. Under U.S. Army Research Office Grant DAAD19-00-1-0177, “Quantum Information Technology: Entanglement, Teleportation, and Quantum Memory,” a team of researchers from the Massachusetts Institute of Technology (MIT) and Northwestern University (NU) have undertaken a Multidisciplinary University Research Initiative (MURI) program to overcome this obstacle. In particular:

(*) We have developed an architecture for long-distance, high-fidelity qubit teleportation that uses a novel ultrabright narrowband source of polarization-entangled photon pairs, and a trapped-atom quantum memory whose loading can be verified nondestructively and whose structure permits all four Bell-state measurements to be performed.

(*) We are working to realize all the technology elements to instantiate our quantum communication architecture, including polarization entanglement sources based on parametric amplifiers or fiber Sagnac loops, long-distance entanglement distribution over standard telecom fiber and qubit storage and processing in trapped Rb-atom quantum memories.

(*) We are working on a variety of new concepts for quantum communication and memory that should greatly increase the likelihood that quantum information technology will have a practical future.

An overview of the MIT/NU program was presented by Professor Shapiro, the program's Principal Investigator. The central thrust of the MIT portion of the program is a singlet-state architecture for long-distance, high-fidelity teleportation. Its essential components, conceived and to be developed by members of the MURI team are: an ultrabright narrowband source of polarization-entangled photon pairs, a trapped-atom quantum memory (PDF), and an architecture for connecting these source and memory elements via standard telecommunication fiber. The second major thrust area for the MIT/NU MURI program is the development of quadrature-based teleportation using a fiber-optic entanglement source. Additional efforts, under this program, will be devoted to a variety of theoretical problems related to the applications of entanglement and quantum communication.

The MIT/NU MURI program underwent a full-day review in October 2002, during its third year of existence. In going forward from that review, the MURI effort was refocused on its core agenda, i.e., technology development and supporting theory for long-distance, high-fidelity qubit teleportation.