Entanglement in quantum optics

David S. Simon, Gregg S. Jaeger, Alexander V. Sergienko

Masahiro Matsuoka

Entangled states and their application in quantum optics are reviewed. First, the entangled states of the position and momentum in the EPR paradox and Bohm's spin version are reviewed. Then, various generation methods of entangled states in optics are described: polarization entanglement, frequency entanglement, and quadruture-phase entanglement. Finally, as their applications, fundamentals of quantum communication and teleportation are explained.

Chen Wei, LIU Yan-Hong, ZHAO Lu-Jie

Quantum entanglement is an important quantum resource.Entanglement of quantum nodes is the foundation for constructing large-scale quantum networks consisting of quantum nodes and quantum channels.In practical applications of quantum information， the ineluctable optical transmission loss， phase diffusion noise， and mixing with the thermal states lead to decoherence and disruption of entangled states， which limit the communication distance and affect the quality of entanglement between quantum nodes.Entanglement distillation， which can extract a small portion highly entangled states from a quantity of weakly entangled states， in addition to overcoming this detrimental problem.By preparing entangled optical mode twice and interfering with atomic ensembles， the establishment of entanglement between atomic ensembles and entanglement distillation based on quantum memory and balanced homodyne detection （BHD） can be achieved.The first-prepared entangled optical fields are mapped into two atomic ensembles via electromagnetically-induced-transparency （EIT） quantum memory to establish entanglement between atomic ensembles.Subsequently， the second-prepared entangled optical fields are then distributed to these two entangled atomic ensembles through quantum channels to implement interference.The transmitted optical fields from two atomic ensembles are detected by BHDs， the detection results below the triggered threshold determine the success or failure.During the distribution process， the entangled optical fields prepared twice passed through optical choppers， which are divided into three different zones according to the requirements， and each zone is glued with different optical components.Zone I does not have any optics， zone Ⅱ has an optical attenuator， and zone Ⅲ is used to block the optical beams.The second-prepared entangled optical fields interfere with these two entangled atomic ensembles through zone Ⅱ， and the transmittance of the optical attenuator directly affects the effect of entanglement distillation.In this paper， we theoretically analyze the effect of different transmittance of optical attenuator on the effect of entanglement distillation， and find the corresponding quantum writing efficiency when the entanglement distillation achieves the best effect.As the transmittance increases， the effect of entanglement distillation is better； when the transmittance is certain， there exists an optimal writing efficiency which makes the entanglement between atomic ensembles optimal.As the transmittance increases gradually， the optimal writing efficiency becomes smaller， which is easier to realize in the experiment.Additionally， the correlation variaces before and after the entanglement distillation of atomic spin waves with other physical parameters are analyzed， which provides a basis for the selection of physical parameters in the entanglement distillation scheme， and lays a foundation for construction of large-scale quantum networks.

Anton Zeilinger, Herbert Joseph Bernstein, Daniel M. Greenberger +2 more

Trond Hjerpekjøn Haug, Anton Frisk Kockum, Raphaël Van Laer

Exploiting the strengths of different quantum hardware components may increase the capabilities of emerging quantum processors. Here we propose and analyze a quantum architecture that leverages the nonlocal connectivity of optics, along with the exquisite quantum control offered by superconducting microwave circuits, to produce entangled optical resource states. In contrast to previous proposals on optically distributing entanglement between superconducting microwave processors, we use squeezing between microwaves and optics to produce microwave-optical Bell pairs in a dual-rail encoding from a single microwave quantum processor. Moreover, the microwave quantum processor allows us to deterministically entangle microwave-optical Bell pairs into larger cluster states, from which entangled optical photons can be extracted through microwave measurements. Our scheme paves the way for small microwave quantum processors to create heralded entangled optical resource states for optical quantum computation, communication, and sensing using imperfect microwave-optics transducers. We expect that improved isolation of the superconducting processor from stray optical fields will allow the scheme to be demonstrated with currently available hardware. Published by the American Physical Society 2024

F. J. Duarte