Squeezing angle locking of entangled microwave based on photon counting

Abstract

Quantum entanglement possesses important applications in quantum computation, quantum communication, and quantum precision measurement. It is also an important method to improve the performance of quantum radar and quantum radio navigation. However, the penetration of light wave is poor due to the high frequency, which leads to detecting limitations in bad weather. In this context, quantum entanglement in the microwave domain has been extensively studied, and it is hopeful to overcome the above-mentioned defects in quantum optics. Although the entangled microwave preparation of continuous variable is achievable at present, there exist still some problems such as poor entanglement performance, low entanglement efficiency, complex signal processing and control, which restrict the development of entangled microwave sources. In order to improve the entanglement performance in microwave domain, a squeezing-angle locking scheme based on single photon counting is proposed. First, two Josephson parametric amplifiers (JPAs) are driven respectively by two pump signals to generate two single-mode squeezed states which are uncorrelated to each other. Next, the squeezing angle difference between the two single-mode squeezed states is adjusted to 180°, and then the two signals are mixed in a superconducting 180° hybrid ring coupler for two entangled microwave outputs. The outputs are single photon detected, and the results are sent to the data processor for solution. The squeezing angle difference between the input single-mode squeezed microwaves is estimated by Bayesian criterion and compared with the target value to calculate the error. Finally, the squeezing angle correction information is fed back into the JPA pump to control the squeezing angle of the single-mode squeezed microwave of the JPA output as well as the relative squeezing angle to reach the target value. Thus, the dual-path entangled microwave with the optimal entanglement performance is output. Comparing with the existing entangled microwave preparation schemes, a single photon counter is utilized in the scheme of this paper, which leads to a detection efficiency of 90%. In addition, the Bayesian criterion is used to estimate the output result, and the theoretical precision reaches the quantum Cramer-Rao lower bound. Meanwhile, the introduced noise level and operation difficulty are reduced, which greatly improves the property of dual-path entangled microwave preparation.

Observation of the performance enhancement of a non-degenerate JPA versus degenerate JPA in a QTMS radar simulation

“…It should be noted that in three-wave pumping (for both DJPA The interesting question raised here is how to separate the signal and idler in the two scenarios of the DJPA and NDJPA in the output of the JPA? The answer is the method of splitting two modes as signal and idler in the degenerate and non-degenerate JPAs is done by using a 180°hybrid ring beam splitter [52,53] and they are completely similar to each other as shown in figures 3 and 1. Therefore, the output of JPAs, both in the case of DJPA and in the case of NDJPA, must be split into two modes by the beam splitter.…”

“…An amplifier circuit can be described generally as a set of simple harmonic modes with time-dependent couplings. The time-dependent effective quadratic Hamiltonian is [26,51,53]:…”