Mixed-state preparation method with adjustable parameters

Abstract

The invention provides a mixed-state preparation method with adjustable parameters. The method comprises an entangled light source preparation part, a weight-adjustable shunt part and decoherence channel parts of all paths, and is characterized in that the entangled light source preparation part is used for preparing entangled photon pairs through a spontaneous parametric down-conversion process generated by using a laser pumping nonlinear crystal; the weight-adjustable shunt part realizes the controllable weight of each path by using a BD crystal network, and a BD crystal divides a non-polarized light beam into two parallel orthogonal polarized light beams; the decoherence channel part of each path introduces a complete mixed state to one path of the entangled photon pair through a controllable decoherence channel. According to the method, a two-photon entangled light source is generated by using BBO crystal spontaneous parametric down-conversion. Through the cascade calcite network,two-bit mixed-state preparation of any parameter can be realized only by adjusting the rotation angle of the half-wave plate. The method is easy to implement. Compared with a mixed state prepared by aSagnac ring interferometer, the method is more stable, more convenient to cascade and modular.

Description

technical field [0001] The invention relates to the technical fields of quantum computing, quantum communication and quantum control, in particular to a method for preparing a mixed state with adjustable parameters. Background technique [0002] Quantum entanglement plays an important role in the quantum world, and it is the core resource of quantum information processing. For example, scientists have completed quantum teleportation, quantum dense coding, quantum computing, and quantum random numbers with the help of entanglement as a resource. However, in the real world, resources such as entanglement are very fragile, and are prone to decoherence with the external environment, which inevitably leads to the degeneration of the prepared quantum state into a mixture of entangled state and fully mixed state. For example, the common Werner state is a typical mixed state. Scientists have realized quantum entanglement purification, quantum hidden non-locality extraction, and qua...

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Problems solved by technology

There are many ways to prepare mixed states in experiments. For example, to prepare two-photon Werner states initially, the most commonly used method is: firstly use spontaneous downparameter conversion to collect the two-photon maximum entangled state, and then use quartz plates to form a decoherent channel, but this The class method can only prepare the Werner state with specific parameters, and the actual preparation operation is more complicated, and the system is not stable

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