Photons and Atoms for Quantum Optical Information

Pieter Kok, Brendon W. Lovett

Mohammad Hafezi, Z. Kim, S. L. Rolston +3 more

A complete physical approach to quantum information requires a robust interface among flying qubits, long-lifetime memory, and computational qubits. Here we present a unified interface for microwave and optical photons, potentially connecting engineerable quantum devices such as superconducting qubits at long distances through optical photons. Our approach uses an ultracold ensemble of atoms for two purposes: quantum memory and to transduce excitations between the two frequency domains. Using coherent control techniques, we examine an approach for converting and storing quantum information between microwave photons in superconducting resonators, ensembles of ultracold atoms, and optical photons, as well as a method for transferring information between two resonators.

Christopher R. Monroe

Jian-Wei Pan

Quantum information science and atom optics are among the most active fields in modern physics. One of our main activities is to use atomic qubits as quantum memory and exploit photonic qubits for information transfer and processing to achieve efficient linear optics quantum information processing (QIP). On the one hand, utilizing the interaction between laser pulses and ultra-cold atomic ensembles we experimentally investigate the potentials of atomic ensembles in the gas phase to build quantum repeaters for long-distance quantum communication, that is, to develop a new technological solution for quantum repeaters making use of the effective qubit-type entanglement of two cold atomic ensembles by a projective measurement of individual photons by spontaneous Raman processes. On the other hand, building on our long experience in research on multi-photon entanglement, The techniques that are being developed will lay the basis for future large-scale realizations of linear optical QIP with atoms and photons.

Pieter Kok, Brendon W. Lovett

We have so far spoken almost exclusively of photons and linear-optical elements, and seen just how powerful those two components can be for information processing. They provide unbreakable cryptographic tools, and allow for efficient quantum computing. However, many more possibilities become available when we allow photons to interact with atoms and solid matter in a quantum mechanical way. In particular, a quantum memory, the principal difficulty for linear-optical quantum computing, can be created. In this chapter we will take the first steps towards a full understanding of a photon's interaction with atoms. We will show how to describe the interactions within a system consisting of photons and few-level atoms and show how this interaction can be manipulated and exploited to provide quantum information processors based on both atomic and photonic qubits. We will also show that photon emission from atoms can degrade the quantum information contained within atoms, and we will present a formalism to model this effect. We begin with a general discussion of atom-photon interactions. Atomic systems as qubits Let us first consider an electron in an isolated atom. It is bound there by the Coulomb force due to the charge distribution of all the other electrons and the nucleus. The potential that describes this coupling is given by V ( r ).

F. E. Becerra