Cross-Phase-Modulation (XPM) For Nonlinear Optical Quantum Computing

Quantum Computing Science is one of the most significant applications of mod-ern Quantum physics. It’s proved that quantum coherence and entanglement can speed up the computing for certain problems, e.g., to break RSA standard for cryptography, as well as be used to build the next-generation computers as the computing scale getting smaller. Photon, as its stable nature, is considered as the candidate for quantum information carriers; which forms the qubit for optical quantum computing, including the linear optical quantum computing (LOQC) and nonlinear optical quantum computing (NLOQC).Cross-Phase Modulation (XPM), based on Kerr nonlinearity, is crucial for NLO-QC since it’s the physical basis for some quantum gates, e.g., CNOT gate. The s-tudy of XPM has shifted from c.w. driving, strong coupling, semi-classical to pulsed, few-photon-level, fully quantized models. Electromagnetically induced transparen-cy (EIT) has been shown useful to generate giant Kerr nonlinearity, especially the double-EIT schemes. However, it’s criticized recently the EIT-based XPM cannot product high-fidelity gate while inducing giant cross-phase shift. In this thesis, we study these issues in details. Particularly, we show that, there are four criteria for efficient XPM gate in quantum computing. The first one is the giant nonlinearity, for which EIT is a good scheme. Secondly, XPM should be based on few or sin-gle photon level, since in quantum computing single photon is used as qubit. The third criteria is the matching for the pulse propagating time, which can be satisfied by double-EIT. Last, the input-output fidelity should be high enough, for which, there is no efficient schemes at present. And we explore the effects of spontaneously generated coherence (SGC) to XPM, and it’s promising that SGC can resolve the trade-off between high fidelity and high cross-phase shift.