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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Optical quantum information processing utilizing weak nonlinearities: a little goes a long way

William J. Munro, Kae Nemoto, Timothy P. Spiller, Raymond G. Beausoleil, Pieter Kok, S. D. Barrett

Published Aug 18, 2005• 3 citations
Publisher

Abstract

Processing information quantum mechanically is known to enable new communication and computational scenarios that cannot be accessed with conventional information technology (IT). It is known that such quantum processing can be performed with linear optical techniques, measurement and feed-forward. However, here the gates are intrinsically probabilistic and so scaling up such an approach requires considerable qubit resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr non-linearities and highly efficient homodyne measurements. This approach enables a parity gate between optical qubits, mediated by an additional optical probe mode, enabling near-deterministic Bell state measurement and entangling gates. Our approach is therefore the basis for very efficient, scalable optical QIP, and provides a natural method for distributing such processing, combining it with quantum communication.

DOI
10.1117/12.613614

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Quantum information offers the promise of being able to perform certain communication and computation tasks that cannot be done with conventional information technology (IT). Optical quantum information processing (QIP) holds particular appeal, since it offers the prospect of communicating and computing with the same type of qubit. Linear optical techniques have been shown to be scalable, but the corresponding quantum computing circuits need many auxiliary resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr nonlinearities and homodyne measurements. We show how this approach provides the fundamental building blocks for highly efficient non-absorbing single photon number resolving detectors, two qubit parity detectors, Bell state measurements and finally near deterministic control-not (CNOT) gates. These are essential QIP devices.
Quantum information processing (QIP) offers the promise of being able to do things that we cannot do with conventional technology. Here we present a new route for distributed optical QIP, based on generalized quantum non-demolition measurements, providing a unified approach for quantum communication and computing. Interactions between photons are generated using weak nonlinearities and intense laser fields—the use of such fields provides for robust distribution of quantum information. Our approach only requires a practical set of resources, and it uses these very efficiently. Thus it promises to be extremely useful for the first quantum technologies, based on scarce resources. Furthermore, in the longer term this approach provides both options and scalability for efficient many-qubit QIP.
Quantum information processing (QIP) offers the promise of being able to do things that we cannot do with conventional technology. Here we present a new route for distributed optical QIP, based on generalized quantum non-demolition measurements, providing a unified approach for quantum communication and computing. Interactions between photons are generated using weak non-linearities and intense laser fields--the use of such fields provides for robust distribution of quantum information. Our approach requires only a practical set of resources, and it uses these very efficiently. Thus it promises to be extremely useful for the first quantum technologies, based on scarce resources. Furthermore, in the longer term this approach provides both options and scalability for efficient many-qubit QIP.
Processing information quantum mechanically is known to enable new communication and computational scenarios that cannot be accessed with conventional information technology (IT). We present here a new approach to scalable quantum computing---a "qubus computer"---which realizes qubit measurement and quantum gates through interacting qubits with a quantum communication bus mode. The qubits could be "static" matter qubits or "flying" optical qubits, but the scheme we focus on here is particularly suited to matter qubits. Universal two-qubit quantum gates may be effected by schemes which involve measurement of the bus mode, or by schemes where the bus disentangles automatically and no measurement is needed. This approach enables a parity gate between qubits, mediated by a bus, enabling near-deterministic Bell state measurement and entangling gates. Our approach is therefore the basis for very efficient, scalable QIP, and provides a natural method for distributing such processing, combining it with quantum communication.
We propose a simplified parity meter for photonic qubits with cross-Kerr nonlinearities, homodyne measurement, and some optical elements. Our scheme has lower error probability than the protocol proposed in Nemoto and Munro [Phys. Rev. Lett. 93, 250502 (2004)]. Based on the present parity meter, we achieve cluster-state preparation, a complete Bell-state analyzer, and quantum teleportation. All of these schemes are nearly deterministic in the regime with little noise and include less optical elements, which makes our schemes more meaningful for large-scale quantum computing.