Experimental nonlinear sign shift for linear optics quantum computation

We have realized the nonlinear sign shift (NS) operation for photonic qubits.This operation shifts the phase of two photons reflected by a beam splitter using an extra single photon and measurement. We show that the conditional phase shift is $(1.05\pm 0.06) \pi$ in clear agreement with theory. Our results show that by using an ancilla photon and conditional detection, nonlinear optical effects can be implemented using only linear optical elements. This experiment represents an essential step for linear optical implementations of scalable quantum computation.Comment: 4 pages, 4 figure

Single-photon generation from a neodymium ion in optical fiber at room temperature

The realization of single-photon generation is important for implementing various quantum information technologies. The use of rare-earth ions in an optical fiber is a promising single photon generation method due to its ability to operate at room temperature as well as the low cost involved. Neodymium ions are especially interesting because the ions are one of the most commercially affordable rare-earth materials in the current industry. The neodymium ion also has the advantage of having a rich energy level structure, which offers several possible wavelengths for emitted single photons from visible to near-telecommunication wavelengths. In this paper, we experimentally demonstrated single-photon generation using an isolated single neodymium ion in tapered silica fiber at room temperature. Our results have significant implications as a platform for low-cost wavelength-selectable single-photon sources and photonic quantum applications.Comment: 7 pages, 5figure

Scaling the stimulated emission of polarization-entangled photons using passive optical components

Bright sources of polarization-entangled photon pairs are essential components for quantum information technologies. In general, it is necessary to introduce a resonator that combines active optical components such as an electric optical modulator to enhance the stimulated emission of polarization-entangled photons. It is technically difficult to perform the time series operation to output the stimulated entangled photons in the resonator by synchronizing laser pulses. In this paper, we propose a scheme to scale up the stimulated emission of polarization-entangled photon pairs using a resonator with only passive optical components. We show the theoretical aspects of the scheme and also perform a proof-of-principle experimental demonstration of the scheme in a double-pass configuration.Comment: 8 pages, 6 figures, Physical Review A to be publishe

New high-efficiency source of photon pairs for engineering quantum entanglement

We have constructed an efficient source of photon pairs using a waveguide-type nonlinear device and performed a two-photon interference experiment with an unbalanced Michelson interferometer. Parametric down-converted photons from the nonlinear device are detected by two detectors located at the output ports of the interferometer. Because the interferometer is constructed with two optical paths of different length, photons from the shorter path arrive at the detector earlier than those from the longer path. We find that the difference of arrival time and the time window of the coincidence counter are important parameters which determine the boundary between the classical and quantum regime. When the time window of the coincidence counter is smaller than the arrival time difference, fringes of high visibility (80$\pm$ 10%) were observed. This result is only explained by quantum theory and is clear evidence for quantum entanglement of the interferometer's optical paths.Comment: 4 pages, 4 figures, IQEC200