Decoherence and Quantum-State Measurement in Quantum Optics

Jino Heo, Min-Sung Kang, Changho Hong +2 more

We present a scheme to encode quantum information (single logical qubit information) into three-photon decoherence-free states, which can conserve quantum information from collective decoherence, via nonlinearly optical gates (using cross-Kerr nonlinearities: XKNLs) and linearly optical devices. For the preparation of the decoherence-free state, the nonlinearly optical gates (multi-photon gates) consist of weak XKNLs, quantum bus (qubus) beams, and photon-number-resolving (PNR) measurement. Then, by using a linearly optical device, quantum information can be encoded on three-photon decoherence-free state prepared. Subsequently, by our analysis, we show that the nonlinearly optical gates using XKNLs, qubus beams, and PNR measurement are robust against the decoherence effect (photon loss and dephasing) in optical fibers. Consequently, our scheme can be experimentally implemented to efficiently generate three-photon decoherence-free state encoded quantum information, in practice.

Harry J. Kimble, O. Carnal, Zhongliang Hu +4 more

Stefan Scheel

In this article we demonstrate that decoherence of nonclassical states of light can be very efficiently used in optical sensor technology. As an example, we consider squeezing degradation of monomode or bipartite quantum states that are in contact with an environment serving as the measurand. The sensitivity of the measuring device will be greatly enhanced when using strongly squeezed states. Moreover, we show that sensitivity-used squeezing measurement is always larger than for absorption measurements. We present an idea for the important application of the measurement of concentration changes in gaseous flows.

Paolo Tombesi, Daniel F. Walls

T. Stewart McKechnie

M. Korobko, Jan Südbeck, S. Steinlechner +1 more

The most efficient approach to laser interferometric force sensing to date uses monochromatic carrier light with its signal sideband spectrum in a squeezed vacuum state. Quantum decoherence, i.e., mixing with an ordinary vacuum state due to optical losses, is the main sensitivity limit. In this Letter, we present both theoretical and experimental evidence that quantum decoherence in high-precision laser interferometric force sensors enhanced with optical cavities and squeezed light injection can be mitigated by a quantum squeeze operation inside the sensor's cavity. Our experiment shows an enhanced measurement sensitivity that is independent of the optical readout loss in a wide range. Our results pave the way for quantum improvements in scenarios where high decoherence previously precluded the use of squeezed light. Our results hold significant potential for advancing the field of quantum sensors and enabling new experimental approaches in high-precision measurement technology.