Hewlett-Packard Development Company, L.p.

Other

Inter-University Research Institute Corporation Research Organization of Information and Systems

Kae Nemoto

William John Munro

Timothy Paul Spiller

Raymond G Beausoleil

Sean D Barrett

Pieter Kok

Keith Alexander Harrison

Yoshihisa Yamamoto

Peter Van Loock

Timothy P Spillar

A method is provided of creating an end-to-end entanglement () between qubits in first and second end nodes () of a chain of optically-coupled nodes whose intermediate nodes () are quantum repeaters. Local entanglements () are created on an on-going basis between qubits in neighboring pairs in the chain through interaction of the qubits with light fields transmitted between the nodes. The quantum repeaters () are cyclically operated with their top-level operating cycles being synchronized. Once every top-level operating cycle, each repeater () initiates a merging of two entanglements involving respective repeater qubits that are at least expected to be entangled with qubits in nodes disposed in opposite directions along the chain from the repeater. A quantum repeater () adapted for implementing this method is also provided.

Quantum repeater and system and method for creating extended entanglements

An iterative method is provided for progressively building an end-to-end entanglement between qubits in first and second end nodes () of a chain of nodes whose intermediate nodes () are quantum repeaters. At each iteration, a current operative repeater () of the chain merges an entanglement existing between qubits in the first end node () and the operative repeater, with a local entanglement formed between qubits in the operative repeater and its neighbor node towards the second end node (). For the first iteration, the operative repeater is the neighbor of the first end node (); thereafter, for each new iteration the operative repeater shifts one node further along the chain toward the second end node (). A quantum repeater adapted for implementing this method is also provided.

A quantum repeater includes a transmitter portion including a source, a set of matter systems, and an optical system. The source produces a probe pulse in a probe state having components with different photon numbers, and each matter system has at least one state that interacts with photons in the probe pulse to introduce a change in a phase space location of the probe state. The optical system can direct the probe pulse for interaction with one of the matter systems and direct light from the matter system for transmission on a first channel.

Quantum repeater

Structures and methods allow: transfer of quantum information represented using the states of light to a representation using the states of matter systems; transfer of quantum information represented by the states of matter systems to a representation using the states of light; and error resistant encoding of quantum information using entangled states of matter and light to minimize errors.

Quantum information conversion between matter and light representations

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

Nonlinear elements can efficiently implement quantum information processing systems such as controlled phase shifters, non-absorbing detectors including parity detectors, quantum subspace projections, non-absorbing Bell state analyzers, non-absorbing encoders/entanglers, and fundamental quantum gates such as CNOT gates. The non-absorbing detectors permit improvements in the efficiency of a probabilistic quantum gate by permitting reuse of the same photonic resources during multiple passes through the probabilistic gate.

Quantum coherent systems and operations

Systems and methods convert or transfer quantum information from one photonic representation or state to another. This permits conversion of quantum information from one encoding to another and to representations that are convenient, efficient, or required for desired manipulations.

Conversion of quantum information from one photonic representation to another photonic representation

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.

Nonlinear electromagnetic quantum information processing

A device capable of efficiently detecting a single-photon signal preserves a photon characteristic such as polarization or angular momentum. The device can include a beam splitter that splits an input photon state into modes that are distinguished by states of a characteristic of signal photons in the input photon state, a non-destructive measurement system capable of measuring a total number of photons in the modes without identifying a photon number for any individual one of the modes; and a beam combiner positioned to combine the modes after output from the non-destructive detection system.

Non-demolition photon detector that preserves input state characteristics

A device capable of efficiently detecting a single-photon signal includes a matter system, sources of a first beam and a second beam, and a measurement system. The matter system has a first energy level and a second energy level such that a signal photon couples to a transition between the first energy level and the second energy level. The first beam contains photons that couple to a transition between the second energy level and a third energy level of the matter system, and the second beam contains photons that couple to a transition between the third energy level and a fourth energy level of the matter system. The measurement system measures a change in the first or second beam to detect the absence, the presence, or the number of the photons in the signal.

Growing community of inventors

Tokyo, Japan

Kae Nemoto