Quantum Phase Measurement and Metrology using Four-Wave Mixing

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Precision optical measurements are limited in sensitivity and resolution by the noise on the light used to make them. In everyday life a classical description of light usually suffices. However taking this approach leads to limitations on the sensitivity of measurements that are not fundamental. If one uses a quantum mechanical description of the light, then one can envision "non-classical" light fields that will lead to more sensitive measurements than with "classical" light. This extra sensitivity can be used for ultrasensitive detection in defense applications and is especially useful at very low light levels. Thus it is interesting in the field of imaging of live biological tissues where one would like to avoid damage to the tissue. This project will use the non-linear optical properties of certain materials to create non-classical light and investigate how much advantage over the limits for classical light can be achieved. In particular, this team has demonstrated an optical phase measurement device that has more sensitivity to length changes than a "classical" interferometer using a laser source. The group will further investigate the design of different quantum-based phase measurement devices and study what aspects of these approaches lead to better measurements. Non-classical light, which has different noise statistics than classical light, will allow this team to make measurements with noise levels that are below those obtainable with a coherent state or other "nearly classical" optical fields. The use of intrinsically quantum states in metrological applications, such as interferometry, will allow the group to improve such measurements beyond what can be obtained with classical light. This team studies how to take advantage of quantum states for noise reduction and demonstrate the usefulness and/or limitations of these states. In particular, this project is centered on studying phase-measurement devices based on "active-media", with gain or stimulated loss. The team will study seeded versions, based on phase measurements using an amplified seed beam, as well as unseeded versions, based on the use of spontaneous emission alone. They plan to both look at these interferometers as phase measurement tools, and as a means to study the quantum states that are internal to these devices. In terms of the quantum states, they will study the effect of directly modulating a quantum state, and in particular, modulating one mode of a two-mode squeezed state.