Dissipative production of a maximally entangled steady state of two quantum bits
Abstract
Entangled states are a key resource in fundamental quantum physics, quantum cryptography and quantum computation. Introduction of controlled unitary processesquantum gatesto a quantum system has so far been the most widely used method to create entanglement deterministically. These processes require highfidelity state preparation and minimization of the decoherence that inevitably arises from coupling between the system and the environment, and imperfect control of the system parameters. Here we combine unitary processes with engineered dissipation to deterministically produce and stabilize an approximate Bell state of two trappedion quantum bits (qubits), independent of their initial states. Compared with previous studies that involved dissipative entanglement of atomic ensembles or the application of sequences of multiple timedependent gates to trapped ions, we implement our combined process using trappedion qubits in a continuous timeindependent fashion (analogous to optical pumping of atomic states). By continuously driving the system towards the steady state, entanglement is stabilized even in the presence of experimental noise and decoherence. Our demonstration of an entangled steady state of two qubits represents a step towards dissipative state engineering, dissipative quantum computation and dissipative phase transitions. Following this approach, engineered coupling to the environment may be applied to a broad range of experimental systems to achieve desired quantum dynamics or steady states. Indeed, concurrently with this work, an entangled steady state of two superconducting qubits was demonstrated using dissipation.
 Publication:

Nature
 Pub Date:
 December 2013
 DOI:
 10.1038/nature12801
 arXiv:
 arXiv:1307.4443
 Bibcode:
 2013Natur.504..415L
 Keywords:

 Quantum Physics;
 Physics  Atomic Physics
 EPrint:
 25 pages, 5 figures