Reconfigurable multi-mode entanglement within one beam

Abstract

New continuous variable quantum protocols such as cluster state computation [1] and quantum error correction [2] require an increasing number of modes to be entangled in a specific way. Conventionally, the entangled modes are carried by as many single mode beams [3, 4]. In order to produce entanglement, each beam of classical light first goes through a single mode optical parametric amplifier (OPA). This OPA reduces the variance of one of the quadratures of one mode of the electromagnetic field below the quantum noise limit (the mode is then called squeezed). The squeezed modes are then mixed together using a specific sequence of beam-splitters of defined ratios. For each beamsplitter, the relative phase of the two input modes is also defined and controlled. To each sequence of beam-splitting ratios and relative phases corresponds a unitary transformation between the input modes and the output modes. This unitary transformation gives a set of sub quantum noise relationships between the output modes quadratures with each protocol defined by a different set of relationships. After the desired entanglement has been produced, homodyne detections are performed on the output modes to implement the protocol. Using one beam per mode is resource heavy and inflexible. We present and characterize an alternative set of tools for flexible, computer reconfigurable, multi-mode entanglement. Show more