title: 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 processes--quantum gates--to a quantum system has so far been the most widely used method to create entanglement deterministically. These processes require high-fidelity 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 trapped-ion 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 time-dependent gates to trapped ions, we implement our combined process using trapped-ion qubits in a continuous time-independent 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.
authors.affiliation: 1] National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA [2].
authors.forename: Y
authors.initials: Y
authors.lastname: Lin
authors.affiliation: 1] National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA [2].
authors.forename: J P
authors.initials: JP
authors.lastname: Gaebler
authors.affiliation: QUANTOP, The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark.
authors.forename: F
authors.initials: F
authors.lastname: Reiter
authors.affiliation: National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Tan
authors.affiliation: National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
authors.forename: R
authors.initials: R
authors.lastname: Bowler
authors.affiliation: QUANTOP, The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark.
authors.forename: A S
authors.initials: AS
authors.lastname: Sørensen
authors.affiliation: National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
authors.forename: D
authors.initials: D
authors.lastname: Leibfried
authors.affiliation: National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Wineland