We present our theoretical and experimental studies of the generation of multimode squeezing and multipartite continuous-variable entanglement, below and above threshold, in an optical parametric oscillator in which several different three-wave mixings are concurrently phase-matched.
In this paper, we investigate the generation of multimode entanglement and squeezing of an optical field via coupled four-wave mixing interactions in a Kerr nonlinear medium pumped at multiple well-separated frequencies. We show that genuine multimode entanglement can be obtained and this entanglement can be verified with the measurable multimode squeezing present in the system. This scheme may be used to achieve entangled frequency combs which are useful in continuous-variable quantum communication networks.
Optical parametric oscillators (OPO) have been extensively used in the continuous variable quantum optics community as a resource to produce non-classical states of light, including squeezed states or entangled beams. In this paper, general description of multimode OPOs is presented, show that they are able to produce a very wide variety of multimode quantum states of light, and give techniques to measure or separate them. The description applies equally to the spatial and temporal configurations, which are experimentally studied in lab.
Nowadays, the realization of quantum computations and communications based on continuous variables has attracted a significant attention due to a substantial expansion of the system dimensionality. The main progress in this area is attributed to the implementation of multimode systems based on squeezed states of light. One of the simplest ways to generate such states relies upon their producing in a single-pass optical parametric amplifier (OPA) using ultrafast pumping. However, for homodyne detection of such multimode states, the profile of the local oscillator (LO) must perfectly match the profile of the measured mode. Usually, this is not the case; therefore a proper treatment of multimode squeezing is required. In this work, we study both theoretically and experimentally the multimode squeezed light generated in type-0 and type-II OPA. We characterize such sources and investigate the degree of squeezing in dependence on the LO spectral profile, employing a pulse shaping technique. The theoretical analysis is performed using the Schmidt-mode theory. This work might have a significant impact on the realization of multimode quantum protocols
We present the first measurement of squeezed-state entanglement between the twin beams produced in an optical parametric oscillator operating above threshold. In addition to the usual squeezing in the intensity difference between the twin beams, we have measured squeezing in the sum of phase quadratures. Our scheme enables us to measure such phase anticorrelations between fields of different frequencies. In the present measurements, wavelengths differ by approximately 1 nm. Entanglement is demonstrated according to the Duan et al. criterion [Phys. Rev. Lett. 84, 2722 (2000)] Delta2p- + Delta2q+ = 1.41(2) < 2. This experiment opens the way for new potential applications such as the transfer of quantum information between different parts of the electromagnetic spectrum.