Parity-swap state comparison amplifier for Schrödinger cat states

We propose a postselecting parity-swap amplifier for Schrödinger cat states that does not require the amplified state to be known a priori. The device is based on a previously implemented state comparison amplifier for coherent states. It consumes only Gaussian resource states, which provides an advantage over some cat state amplifiers. It requires simple Geiger-mode photodetectors and works with high fidelity and approximately twofold gain

Ghost displacement

We describe a technique whereby a coherent amplitude can be imprinted nonlocally on to a beam of light with thermal statistics that has no phase information on average. We have successfully performed the first experimental realisation. The technique could have applications in the sharing of quantum information and in covert quantum imaging scenarios

Covert information sharing via ghost displacement

Ghost imaging research has demonstrated that it is possible to reproduce an image of an object that has not interacted with the imaging light. In this paper we describe theoretically and demonstrate experimentally a coherent displacement imposed nonlocally on one mode of a two-mode state, replicating the ghost imaging effect in the coherent-state basis. We use it to show the possibility of a form of covert information sharing via a ghost displacement operation which enables two distant users to retrieve amplitude and phase information modulated onto a phase-independent thermal state, based only on correlated detection statistics. The displacement operation also provides a secondary probabilistic amplification effect on the mean photon number of the displaced thermal state, which could be exploited for covert quantum illumination experiments

Manipulating thermal light via displaced-photon subtraction

Thermal radiation played a pivotal role in the preliminary development of quantum physics where it helped resolve the apparent incongruity of the ultraviolet catastrophe. In contemporary physics, thermal state generation and manipulation finds new application in fields such as quantum imaging and quantum illumination and as a practical realization of Maxwell's demon. These applications often go hand in hand with photon subtraction operations which probabilistically amplify the mean photon number (MPN) of thermal light as a result of its super-Poissonian photon statistics. In this article, we introduce an operation for thermal states of light based on a generalized photon subtraction scheme. Displaced-photon subtraction (DPS) makes use of coherent state displacement followed by a subsequent anti-displacement in combination with single-photon detection to probe the MPN of a thermal state. We find regimes in which the output of a successful DPS is amplified, unchanged, or attenuated relative to the unconditioned output state. The regime of operation is controlled via the magnitude of the coherent displacement. A theoretical description of generalized photon subtraction of a displaced thermal state is derived via a two-mode moment-generating function (MGF) and used to describe generalized DPS. We perform a proof of principle experimental implementation of DPS for the case of a balanced beam splitter for which results demonstrate good agreement with the model

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