This PDF file contains the front matter associated with SPIE Proceedings Volume 6906, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The frequency comb of an optical resonator is a naturally large set of exquisitely well defined quantum systems, such as in the broadband mode-locked lasers which have redefined time/frequency metrology and ultraprecise measurements in recent years. High coherence can therefore be expected in the quantum version of the frequency comb, in which nonlinear interactions couple different cavity modes, as can be modeled by different forms of graph states. We show that is possible to thereby generate states of interest to quantum metrology and computing, such as multipartite entangled cluster and Greenberger-Horne-Zeilinger states.

It is known that the phase measurement using lossless Mach-Zehnder interferometer with certain entangled N-photon states can achieve a phase sensitivity of the order of 1/N, the Heisenberg limit. However, the output observable used is different for different input states to achieve the Heisenberg limit. In this paper, we show that it is possible to achieve this limit just by parity measurement for all the commonly proposed entangled states. Taking account of path absorption effect, the phase shifts with parity measurement for these states are obtained and indicate that the N00N state still remains to be the best candidate to perform phase detection if the transmittance of the medium is not too small and the number of photons is not very large.

We report observation of high contrast Raman-Ramsey fringes using time delayed optical pulse pairs in a rubidium vapor cell. The width of these fringes are not limited by saturation and provides a simpler means to produce narrow atomic linewidths using a thermal vapor medium for compact atomic clock applications. We also demonstrate phasescanned Raman-Ramsey fringes, with potential application to sensitive detection of trace vapors.

The end-resonance clock uses strong hyperfine end transition to stabilize the frequency of the local oscillator. Comparing to the conventional 0-0 atomic clock, end resonance has very small spin-exchange broadening effect. The spin-exchange rate is proportional to the number density of the alkali-metal atoms. By using the end resonance, we are able to use very high dense vapor to obtain a much better signal to noise ratio. On the other hand, the end resonance suffers from the first-order magnetic field dependence. This problem, however, can be solved by simultaneously using a Zeeman end resonance to stabilize the magnetic field. Here, we report the most recent result of the end-resonance clock. In addition, we report a whole new technique, push-pull laser-atomic oscillator, which can be thought as all-photonic clock. This new clock requires no local oscillator. It acts like a photonic version of maser, which spontaneously generates modulated laser light and modulated voltage signals. The modulation serves as the clock signal, which is automatically locked to the ground-state hyperfine frequency of alkali-metal atoms.

We analyze the phase estimation ability of photonic N00N states propagating in a lossy medium. In such a medium a N00N state of N enangled photons cannot achieve the maximum 1/N phase estimation resolution. In fact, unless the transmittance of the medium is extremely high, a signal comprised of an attenuated separable state of N photons will produce a better phase estimate than a comparable signal of an equally attenuated N00N state. Thus, for most practical applications the resolution provided photonic N00N states is actually worse than the 1/√N Standard Quantum Limit. This performance deficit becomes more pronounced as the number of photons in the signal increases.

In this paper, we study theoretically a zero-area Sagnac ring laser gravitational wave (GW) detector. We review first the zero-area Sagnac interferometer for GW detection, comparing its properties against the more conventional GW detector based on a Michaelson interferometer. We then describe a modified version of such a detector where the Sagnac interferometer is replaced by a zero-area Sagnac ring resonator fed by an external laser. This leads to the description of a GW detector based on an active, zero-area Sagnac ring resonator, where a gain medium is present inside the cavity. Finally, we show that if a medium with negative dispersion, which yields the so-called fast-light effect, is also present inside this detector, then its sensitivity to GW strain is enhanced by the inverse of the group index of the dispersive medium. We describe conditions under which this enhancement factor could be as large as 10⁵.

Radiation pressure exerted by light in interferometric measurements is responsible for displacements of mirrors which appear as an additional back-action noise and limit the sensitivity of the measurement. We experimentally study these effects by monitoring in a very highfinesse optical cavity the displacements of a mirror with a sensitivity at the 10^-20 m/√Hz level. This unique sensitivity is a step towards the first observation of the fundamental quantum effects of radiation pressure and the resulting standard quantum limit in interferometric measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes, and we already report the first experimental demonstration of a back-action noise cancellation. Using a classical radiation-pressure noise to mimic the quantum noise of light, we have observed a drastic improvement of sensitivity both in position and force measurements.

General requirements for single-photon devices in various applications are presented and compared with experimental progress to date. The quantum information applications that currently appear the most promising require a matter qubit-enabled single-photon source, where the emitted photon state is linked to the state of a long-lived quantum system such as an electron spin. The nitrogen-vacancy center in diamond is a promising solid-state system for realizing such a device due to its long-lived electron spin coherence, optical addressability, and ability to couple to a manageable number of nuclear spins. This system is discussed in detail, and experimental results from our laboratory are shown. A critical component of such a device is an optical microcavity to enhance the coupling between the nitrogen-vacancy center and a single photon, and we discuss theoretically the requirements for achieving this enhancement.