Quantum computation using linear optics nd single photons

T. B. Pittman, B. C. Jacobs, J. D. Franson

Kiraz, Mete Atatüre, Imamoglu

Timothy C. Ralph, Austin P. Lund, Howard M. Wiseman

Photon counting induces an effective non-linear optical phase shift in certain states derived by linear optics from single photons. Although this non-linearity is non-deterministic, it is sufficient in principle to allow scalable linear optics quantum computation (LOQC). The most obvious way to encode a qubit optically is as a superposition of the vacuum and a single photon in one mode—so-called ‘single-rail’ logic. Until now this approach was thought to be prohibitively expensive (in resources) compared to ‘dual-rail’ logic where a qubit is stored by a photon across two modes. Here we attack this problem with real-time feedback control, which can realize a quantum-limited phase measurement on a single mode, as has been recently demonstrated experimentally. We show that with this added measurement resource, the resource requirements for single-rail LOQC are not substantially different from those of dual-rail LOQC. In particular, with adaptive phase measurements an arbitrary qubit state can be prepared deterministically .

Shigeki Takeuchi

A quantum computer that gives us the result of a single quantum computation has been constructed. The quantum register was realized by modes and polarization of photons, and the unitary transformation was implemented with linear optics. For each quantum computation, the answer to the Deutsch Jozsa problem for any four-bit digit is given by a single-photon detection signal with a small error rate of less than 4%.

Nobuyuki Matsuda

Shigeki Takeuchi

A quantum computation algorithm is demonstrated using single photons and linear optics. Quantum registers are realized by modes and polarization of photons, and the unitary transformations for them are implemented with linear optics. For each quantum computation, the answer to the Deutsch Jozsa problem for any 4 bit digit is given by a single-photon detection signal with a small error rate. The origin of the error is also studied and categorized according to the sources: systematic errors of quantum gates, phase relaxation, amplitude dumping, and misreadout. It is suspected that a demonstration of 11 qubits using linear optics anda single photon with less than a 20 % error rate is achievable by the technique used in the experiment. As a further objective, an idea to construct controlled-NOT gate using quantum phase gate (QPG) given by Chuang et. al., is introduced and experiments on the QPGs are also reviewed.