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arXiv:1206.1870 · Physical Review A

Proposal for exploring macroscopic entanglement with a single photon and coherent states

Pavel Sekatski, Nicolas Sangouard, Magdalena Stobińska, Félix Bussières, Mikael Afzelius, Nicolas Gisin

Published Dec 3, 2012• 65 citations
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Abstract

Entanglement between macroscopically populated states can easily be created by combining a single photon and a bright coherent state on a beamsplitter. Motivated by the simplicity of this technique, we report on a method using displacement operations in the phase space and basic photon detections to reveal such an entanglement. We show that this eminently feasible approach provides an attractive way for exploring entanglement at various scales, ranging from 1 to 1000 photons. This offers an instructive viewpoint to gain insight into why it is hard to observe quantum features in our macroscopic world.

DOI
10.1103/physreva.86.060301

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Entanglement between macroscopically populated states can easily be created by combining a single photon and a bright coherent state on a beamsplitter. Motivated by the simplicity of this technique, we report on a method using displacement operations in the phase space and basic photon detections to reveal such an entanglement. We show that this eminently feasible approach provides an attractive way for exploring entanglement at various scales, ranging from 1 to 1000 photons. This offers an instructive viewpoint to gain insight into why it is hard to observe quantum features in our macroscopic world.
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A method for exploring photon-number entangled states with weak nonlinearities is described. We show that it is possible to create and detect such entanglement at various scales, ranging from microscopic to macroscopic systems. In the present architecture, we suggest that the maximal phase shift induced in the process of interaction between photons is proportional to photon numbers. Also, in the absence of decoherence we analyze maximum error probability and show its feasibility with current technology.
Tremendous progress has been realized in quantum optics for engineering and detecting the quantum properties of light. Today, photon pairs are routinely created in entangled states. Entanglement is revealed using single-photon detectors in which a single photon triggers an avalanche current. The resulting signal is then processed and stored in a computer. Here, we propose an approach to get rid of all the electronic devices between the photons and the experimentalist, i.e., to use the experimentalist’s eye to detect entanglement. We show in particular that the micro-entanglement that is produced by sending a single photon into a beam splitter can be detected with the eye using the magnifying glass of a displacement in phase space. The feasibility study convincingly demonstrates the possibility of realizing the first experiment where entanglement is observed with the eye.
Displaced single-photon entanglement is a simple form of optical entanglement, obtained by sending a photon on a beam splitter and subsequently applying a displacement operation. We show that it can generate, through a momentum transfer in the pulsed regime, an optomechanical entangled state involving macroscopically distinct mechanical components, even if the optomechanical system operates in the single-photon weak coupling regime. We discuss the experimental feasibility of this approach and show that it might open up a way for testing unconventional decoherence models.
Schrödinger's famous Gedankenexperiment has inspired multiple generations of physicists to think about apparent paradoxes that arise when the logic of quantum physics is applied to macroscopic objects. The development of quantum technologies enabled us to produce physical analogues of Schrödinger's cats, such as superpositions of macroscopically distinct states as well as entangled states of microscopic and macroscopic entities. Here we take one step further and prepare an optical state which, in Schrödinger's language, is equivalent to a superposition of two cats, one of which is dead and the other alive, but it is not known in which state each individual cat is. Specifically, the alive and dead states are, respectively, the displaced single photon and displaced vacuum (coherent state), with the magnitude of displacement being on a scale of 10810^8108 photons. These two states have significantly different photon statistics and are therefore macroscopically distinguishable.