Hewlett-packard Development Company, L.p.

Pieter Kok

William John Munro

Sean D Barrett

Raymond G Beausoleil

Timothy Paul Spiller

Kae Nemoto

Timothy P Spillar

Various embodiments of the present invention are directed to methods for generating an entangled state of qubits. In one embodiment of the present invention, a method for preparing an entangled state of qubits comprises providing a probe and N non-interacting qubits, each qubit comprises a linear superposition of two basis states. The probe is transmitted into an interaction region that separately couples the probe to each of the qubits and produces a number of different probes. A linear superposition of states is output from the interaction region, each state in the linear superposition of states comprises a tensor product of entangled basis states and one of the different probes. The linear superposition of states is projected into one of the entangled states by measuring the state of the probe.

Methods for preparing entangled quantum states

The states of matter system () having only ones basis state that couples to an excited state can be entangled using measurements of photons during transitions from the excited state. High efficiency of entanglement operation can be achieved by repeating the measurements after performing bit flips on the matter systems (). High efficiency of entanglement operation can be achieved using non-absorbing parity measurements on the emitted photons so that measured photons can be subsequently manipulated and measured to near-deterministically produce entangled states. Such entanglement operations can be employed to construct cluster states suitable for simulating arbitrary logic networks.

Entanglement processes and system

Various embodiments of the present invention are directed to methods for determining a phase shift acquired by an entangled N-qubit system represented by a NOON state. In one embodiment, a probe electromagnetic field is coupled with each qubit system. The phase shift acquired by the qubit systems is transferred to the probe electromagnetic field by transforming each qubit-system state into a linear superposition of qubit basis states. An intensity measurement is performed on the probe electromagnetic field in order to obtain a corresponding measurement result. A counter associated with a measurement-result interval is incremented, based on the measurement result falling within the measurement-result interval. A frequency distribution is produced by normalizing the counter associated with each measurement-result interval for a number of trials. The phase shift is determined by fitting a probability distribution associated with the probe electromagnetic field to the frequency distribution as a function of the phase shift.

Methods for determining relative phase differences in entangled quantum states

Nonlinear electromagnetic elements can efficiently implement quantum information processing tasks such as controlled phase shifts, non-demolition state detection, quantum subspace projections, non-demolition Bell state analysis, heralded state preparation, quantum non-demolition encoding, and fundamental quantum gate operations. Direct use of electromagnetic non-linearity can amplify small phase shifts and use feed forward systems in a near deterministic manner with high operating efficiency. Measurements using homodyne detectors can cause near deterministic projection of input states on a Hilbert subspace identified by the measurement results. Feed forward operation can then alter the projected state if desired to achieve a desired output state with near 100% efficiency.

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Cardiff, United Kingdom

Pieter Kok