Photon-recoil and laser-focusing limits to Rydberg gate fidelity
Photon-recoil and laser-focusing limits to Rydberg gate fidelity
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DOI：
10.1103/physreva.103.022424
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发表时间：
2020-11
期刊：
影响因子：
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通讯作者：
F. Robicheaux;T. Graham;M. Saffman
中科院分区：
文献类型：
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作者：
F. Robicheaux;T. Graham;M. Saffman
量化了由中性原子内态与运动自由度的纠缠引起的里德堡门保真度极限，这些自由度是由光子吸收和再发射的动量踢引起的。当原子处于内部状态的叠加，但其中只有一个状态受到可见光或紫外光光子的操纵时，就会发生这种情况。给出了描述这种情况的薛定谔方程，并讨论了两种情况。在第一种情况下，纠缠的产生是由于激发和受激发射在时间上的分离导致空间波函数的漂移。对于谐振子陷阱中的中性原子，当激光脉冲的持续时间短于谐振子周期时，退相干可以在突然近似下表示。在这个极限下，退相干是由简单的解析公式给出的，这些公式考虑了光子的动量、原子的温度、谐振子频率和原子质量。在第二种情况下，由于引起吸收和受激发射的光子处于聚焦光束模式，因此栅保真度降低。这导致了光致内态变化与质心原子位置的依赖关系。在脉冲间隔时间较短的极限情况下，退相干可以表示为一个简单的解析式，它涉及激光束腰、原子温度、陷阱频率和原子质量。研究了标准Rydberg门和基于高斯包络的单个绝热脉冲的新协议对门保真度的影响。
Limits to Rydberg gate fidelity that arise from the entanglement of internal states of neutral atoms with the motional degrees of freedom due to the momentum kick from photon absorption and re-emission is quantified. This occurs when the atom is in a superposition of internal states but only one of these states is manipulated by visible or UV photons. The Schrodinger equation that describes this situation is presented and two cases are explored. In the first case, the entanglement arises because the spatial wave function shifts due to the separation in time between excitation and stimulated emission. For neutral atoms in a harmonic trap, the decoherence can be expressed within a sudden approximation when the duration of the laser pulses are shorter than the harmonic oscillator period. In this limit, the decoherence is given by simple analytic formulas that account for the momentum of the photon, the temperature of the atoms, the harmonic oscillator frequency, and atomic mass. In the second case, there is a reduction in gate fidelity because the photons causing absorption and stimulated emission are in focused beam modes. This leads to a dependence of the optically induced changes in the internal states on the center of mass atomic position. In the limit where the time between pulses is short, the decoherence can be expressed as a simple analytic formula involving the laser waist, temperature of the atoms, the trap frequency and the atomic mass. These limits on gate fidelity are studied for the standard $\pi-2\pi-\pi$ Rydberg gate and a new protocol based on a single adiabatic pulse with Gaussian envelope.