Entanglement Generated by Dissipation and Steady State Entanglement of Two Macroscopic Objects

Abstract

Entanglement is a striking feature of quantum mechanics and an essential ingredient in most applications in quantum information. Typically, coupling of a system to an environment inhibits entanglement, particularly in macroscopic systems. Here we report on an experiment, where dissipation continuously generates entanglement between two macroscopic objects. This is achieved by engineering the dissipation using laser-and magnetic fields, and leads to robust event-ready entanglement maintained for 0.04s at room temperature. Our system consists of two ensembles containing about 10 12 atoms and separated by 0.5m coupled to the environment composed of the vacuum modes of the electromagnetic field. By combining the dissipative mechanism with a continuous measurement, steady state entanglement is continuously generated and observed for up to an hour. PACS numbers:To date, experiments investigating quantum superpositions and entanglement are hampered by decoherence. Its effects have been studied in several systems [1]. However, it was recognized [2] that the engineered interaction with a reservoir can drive the system into a desired steady state. In particular, dissipation common for two systems can drive them into an entangled state [3]. The idea of using and engineering dissipation rather than relying on coherent evolutions only, represents a paradigm shift with potentially significant practical advantages. Contrary to other methods, entanglement generation by dissipation does not require the preparation of a system in a particular input state and exists, in principle, for an arbitrary long time, which is expected to play an important role in quantum information protocols [4][5][6][7]. These features make dissipative methods inherently stable against weak random perturbations, with the dissipative dynamics stabilizing the entanglement.We report on the first demonstration of purely dissipative entanglement generation [8]. In contrast to previous approaches [9][10][11], entanglement is obtained without using measurements on the quantum state of the environment (i.e. the light field). The dissipation-based method implemented here is deterministic and unconditional and therefore fundamentally different from standard approaches such as the QND-based method [9] or the DLCZ protocol [4], which yield a separable state if the emitted photons are not detected. Furthermore, we report the creation of a steady state atomic entanglement by combining the dissipative mechanism proposed in [12] with continuous measurements. The generated entanglement is of the EPR type, which plays a central role in continuous variable quantum information processing [6,13], quantum sensing [14] and metrology [11,15,16]. Fig. 1a presents the principles of engineered dissipation in our system consisting of two 133 Cs ensembles, interacting with a y-polarized laser field at ω L . A pair of twolevel systems is encoded in the 6S 1/2 ground state sublevels |↑ I ≡ |4, 4 I , |↓ I ≡ |4, 3 I and |↑ II ≡ |4, −3 II , |↓ II ≡ |4, −4 II . Operators J ± I/II with J ...

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