Abstract
The non-measurement based coherent feedback control (CFC) is a control method without introducing any backaction noise into the controlled system, thus is specially suitable to manipulate various quantum optical systems for preparing nonclassical states of light. By simply tuning the transmissivity of an optical controller in a CFC loop attached to a non-degenerate optical parametric amplifier (NOPA), the quantum entanglement degree of the output optical entangled state of the system is improved. At the same time, the threshold pump power of the NOPA is reduced also. The experimental results are in reasonable agreement with the theoretical expectation.
Highlights
In recent years, quantum control theory has been widely used in various protocols of quantum optics research[1,2,3,4,5]
The experiment shows that the entanglement degree of the entangled state produced by a non-degenerate optical parametric amplifier (NOPA) can be manipulated by a tunable beam splitter in coherent feedback control (CFC) loop and the entanglement up to − 6.0 dB is obtained
The output entangled state aout s (i) from the NOPA is injected in a CFC control loop composed of two mirrors (M and M0) and a control beam splitter (CBS) with the transmissivity T
Summary
Quantum control theory has been widely used in various protocols of quantum optics research[1,2,3,4,5]. The phase-sensitive manipulation of entangled state of light was theoretically proposed and experimentally realized[19,20,21]. Because there is no measurement element in CFC, i.e. no the access noise, the CFC is a excellent approach to implement the manipulation of the noise-sensitive optical squeezed or entangled states. The enhancement of squeezing of optical field based on CFC was proposed and experimentally realized, which proved the applicability of the CFC in nonclassical regime[11,22,23,24,25]. A scheme of manipulating the multipartite entangled states of light through CFC was theoretically proposed and detailedly analyzed by our group[26]. The output entangled state asou(it) from the NOPA is injected in a ( ) CFC control loop. The advantages and the restrictions of the CFC scheme are discussed
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