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Optical Qubits

Optical Qubits. Li Wang Physics 576 3/9/2007. Q.C. Criteria. Scalability: OK Initialization to fiducial state: Easy Measurement: Problematic Long decoherence time: Good Single Qubit manipulation: Good Conversion to stationary qubit: OK Transmitting between locations: Good

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Optical Qubits

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  1. Optical Qubits Li Wang Physics 576 3/9/2007

  2. Q.C. Criteria • Scalability: OK • Initialization to fiducial state: Easy • Measurement: Problematic • Long decoherence time: Good • Single Qubit manipulation: Good • Conversion to stationary qubit: OK • Transmitting between locations: Good • Entangling gates

  3. Optical Qubit Fiducial state prepare using PBS

  4. State characterization • Impossible to determine polarization with single measurement (Uncertainty principle) • Statistical measurements using many photons • Most measurements depend on coincidence detection – many photons are discarded

  5. State preparation • Using optical elements like HWP and QWP to prepare a specific state • Fidelity > 99.7%

  6. State preparation • Example: Hadamard gate • HWP set to 22.5o of the polarization

  7. Optical CNOT gate • Optical interference from different pathways (O’Brien 2003 Nature) • Ability to produced entangled states (Bell states) Photon in C1 causes Pi phase shift in upper arm of interferometer.

  8. Conversion to stationary qubit • Shown using trapped Cadmium ions (Blinov 2004 Nature)

  9. Non-demolition measurements • Building long distance quantum networks: Quantum repeaters • Entanglement between photon number n and phase Refractive index of the Kerr crystal is changed by intensity of the Signal beam, thus altering the phase of the Meter beam

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