Abstract: In the field of optical quantum information processing, manipulation of single photon qubits in frequency modes employs a frequency beamsplitter employs an asymmetric two-path interferometer, reversible down to the quantum limit. A first partially transmitting mirror splits photons into first and second paths. A time delay element introduces a differential time delay into the second path. And a second partially transmitting mirror mixes the two paths again to form two outputs. A half-wave plate utilizes two of the beam splitters.

Abstract: A method and apparatus for quantum information processing is disclosed in which logical qubits |0>L and |1>L are respectively encoded by different near orthogonal coherent states |?> and |?>, where <?|?>=0, |?> and |?> being the computational basis states for the qubits, for example, in which logical qubits |0>L and |1>L are respectively encoded by different ones of the vacuum state |0> and a multi-photon optical coherent state |?> which states are the computational basis states for the qubits. This provide an efficient scheme for linear optics quantum processing which is deterministic and for which qubit readout can use homodyne detection which is highly efficient. The invention finds application in quantum computation and quantum communication.

Abstract: A nondeterministic quantum CNOT gate (10) for photon qubits, with success probability 1/9, uses beamsplitters (B1–B5) with selected reflectivities to mix control and target input modes. It may be combined with an atomic quantum memory to construct a deterministic CNOT gate, with applications in quantum computing and as a Bell-state analyser.

Abstract: A method and apparatus for quantum information processing is disclosed in which logical qubits |0>L and |1>L are respectively encoded by different near orthogonal coherent states |&bgr;> and |&agr;>, where <&agr;|&bgr;>=0, |&agr;> and |&bgr;> being the computational basis states for the qubits, for example, in which logical qubits |0>L and |1>L are respectively encoded by different ones of the vacuum state |0> and a multi-photon optical coherent state lot>which states are the computational basis states for the qubits. This provide an efficient scheme for linear optics quantum processing which is deterministic and for which qubit readout can use homodyne detection which is highly efficient. The invention finds application in quantum computation and quantum communication.

Abstract: A nondeterministic quantum CNOT gate (10) for photon qubits, with success probability {fraction (1/9)}, uses beamsplitters (B1-B5) with selected reflectivities to mix control and target input modes. It may be combined with an atomic quantum memory to construct a deterministic CNOT gate, with applications in quantum computing and as a Bell-state analyser.