The dynamic encircling of the exceptional point for entangled states and realization. (IMAGE)
Caption
The dynamic encircling of the exceptional point for entangled states and realization. a, the schematic of the quantum walk evolution operator. b, Riemann energy surface for evolution operator Ui. Four stars with different colors represent different initial states. A green ball indicates the position of the exceptional point (EP). c, experimental setup. It consists of three parts, state preparation by the Source; the implementation of the encircling evolution around the exceptional point by the Evolution; and the results obtained by the Measurement. During the state preparation, the quantum states of the two particles are encoded in the horizontal and vertical polarization states of the two photons. In the evolution, the rotation operator R(θ) is implemented using a combination of a green HWP at 0° and a black HWP at θ . Two QWPs and one HWP together implement the conditional phase shift operator S. The partially polarizing beam splitters (PPBS) are used to implement the equivalent gain-loss operator. A combination of two QWPs and one HWP is placed at the end of each step to realize the symmetry-breaking operator ψ(φ) . For different Mn, by changing the parameters θ1 and φ, the loop around the EP is implemented experimentally. For the last operation CN, it is decomposed into the product of a SWAP gate, controlled-not (CNOT) gate, and the operator T. For the measurement, the output state is obtained through two-photon quantum state tomography. d and e, experimental results of the chiral entanglement switching with encircling an EP. The asymmetric convention of entangled states can be found with the clockwise encircling or the counter-clockwise encircling, respectively.
Credit
by Zan Tang, Tian Chen, Xing Tang, and Xiangdong Zhang
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CC BY