Single-photon Kerr nonlinearities do not help quantum computation
- Massachusetts Institute of Technology, Research Laboratory of Electronics, Cambridge, Massachusetts 02139 (United States)
By embedding an atom capable of electromagnetically induced transparency inside an appropriate photonic-crystal microcavity it may become possible to realize an optical nonlinearity that can impart a {pi}-rad-peak phase shift in response to a single-photon excitation. Such a device, if it operated at high fidelity, would then complete a universal gate set for all-optical quantum computation. It is shown here that the causal, noninstantaneous behavior of any {chi}{sup (3)} nonlinearity is enough to preclude such a high-fidelity operation. In particular, when a single-photon-sensitive {chi}{sup (3)} nonlinearity has a response time that is much shorter than the duration of the quantum computer's single-photon pulses, essentially no overall phase shift is imparted to these pulses by cross-phase modulation. Conversely, when this nonlinearity has a response time that is much longer than this pulse duration a single-photon pulse can induce a {pi}-rad overall phase shift through cross-phase modulation, but the phase noise injected by the causal, noninstantaneous response function precludes this from being a high-fidelity operation.
- OSTI ID:
- 20787451
- Journal Information:
- Physical Review. A, Vol. 73, Issue 6; Other Information: DOI: 10.1103/PhysRevA.73.062305; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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