Quantum feedback: Theory, experiments, and applications

The displacement of micro-electro-mechanical-systems (MEMS) cantilevers is used to measure a broad variety of phenomena in devices ranging from force microscopes to biochemical sensors to thermal imaging systems. We demonstrate, to the best of our knowledge, the first direct measurement of a MEMS cantilever displacement with a noise floor 4 dB below the shot-noise limit (SNL) at an equivalent optical power. By combining multi-spatial-mode quantum light sources with a simple differential measurement, we show that sub-SNL MEMS displacement sensitivity is highly accessible compared to previous efforts that measured the displacement of macroscopic mirrors with very distinct spatial structures crafted with multiple optical parametric amplifiers and locking loops. These results support a new class of quantum MEMS sensors with an ultimate signal-to-noise ratio determined by quantum correlations, enabling ultratrace sensing, imaging, and microscopy applications in which signals were previously obscured by shot noise.

Ultrasensitive measurement of microcantilever displacement below the shot-noise limit

The displacement of micro-electro-mechanical-systems (MEMS) cantilevers is used to measure a broad variety of phenomena in devices ranging from force microscopes to biochemical sensors to thermal imaging systems. We demonstrate the first direct measurement of a MEMS cantilever displacement with a noise floor at 40% of the shot noise limit (SNL). By combining multi-spatial-mode quantum light sources with a simple differential measurement, we show that sub-SNL MEMS displacement sensitivity is highly accessible compared to previous efforts that measured the displacement of macroscopic mirrors with very distinct spatial structures crafted with multiple optical parametric amplifiers and locking loops. These results support a new class of quantum MEMS sensor with an ultimate signal to noise ratio determined by quantum correlations, enabling ultra-trace sensing, imaging, and microscopy applications in which signals were previously obscured by shot noise.

Ultrasensitive measurement of MEMS cantilever displacement sensitivity below the shot noise limit

Many emerging quantum technologies demand precise engineering and control over networks consisting of quantum mechanical degrees of freedom connected by propagating electromagnetic fields, or quant...

https://tandfonline.com/doi/pdf/10.1080/23746149.2017.1343097

The SLH framework for modeling quantum input-output networks

We demonstrate compact and accessible squeezed-light magnetometry using four-wave mixing in a single hot rubidium vapor cell. The strong intrinsic coherence of the four-wave mixing process results in nonlinear magneto-optical rotation (NMOR) on each mode of a two-mode relative-intensity squeezed state. This framework enables 4.7 dB of quantum noise reduction while the opposing polarization rotation signals of the probe and conjugate fields add to increase the total signal to noise ratio.

Nonlinear optical magnetometry with accessible in situ optical squeezing

Using a nondegenerate four-wave mixing process in hot rubidium vapor, we demonstrate a compact diode-laser-pumped system for the generation of intensity-difference squeezing down to 8 kHz with a maximum squeezing of −7 dB. To the best of our knowledge, this is the first demonstration of kilohertz-level intensity-difference squeezing using a semiconductor laser as the pump source. This scheme is of interest for experiments involving atomic ensembles, quantum communications, and precision measurements. The diode-laser-pumped system would extend the range of possible applications for squeezing due to its low cost, ease of operation, and ease of integration.

Compact diode-laser-pumped quantum light source based on four-wave mixing in hot rubidium vapor

We experimentally demonstrate optical logic “or” and “nor” gates via coherent feedback. Based on a four-wave mixing process in hot rubidium vapor, two feedback beams are capable of fulfilling an optical “nor” gate for the feedback-suppressed state and an optical “or” gate for the feedback-boosted state simultaneously. The logic gates exhibit transition times faster than previously demonstrated in rubidium vapor. Coherent photon conversion between the two logic states, due to the atomic coherence, is observed in the coherent feedback process.

Optical logic gates using coherent feedback

An all-optical transistor (AOT) is a device in which one light beam can efficiently manipulate another. It is the foundational component of an all-optical communication network. An AOT that can operate at ultralow light levels is especially attractive for its potential application in the quantum information field. Here, we demonstrate an AOT driven by a weak light beam with an energy density of 2.5 × 10−5 photons/(λ2/2π) (corresponding to 6  yJ/(λ2/2π) and about 800 total photons) using the double-Λ four-wave mixing process in hot rubidium vapor. This makes it a promising candidate for ultralow-light-level optical communication and quantum information science.

Ultralow-light-level all-optical transistor in rubidium vapor

The utility model discloses an optical logic gate device based on coherent feedback. The optical logic gate device based on the coherent feedback comprises a laser, polarization splitters, a medium unit, logic control gates, an optical fiber coupling frame and a multimode fiber. Pump light emitted by the laser is reflected by a first polarization splitter and then sequentially shoots into the medium unit and a second polarization splitter to form an annular light spot and two bright spots in the vertical direction. Light beams of the bright spots form two bundles of feedback light through a third polarization splitter. A first logic control gate is arranged along an optical path of the first bundle of feedback light, a second logic control gate is arranged along an optical path of the second bundle of feedback light, the two bundles of feedback light sequentially pass through the optical fiber coupling frame and the multimode fiber and shoot in the first polarization splitter respectively through the first logic control gate and the second logic control gate, and the two bundles of feedback light are intersected with the pump light in the medium unit. The optical logic gate device based on the coherent feedback can achieve optical logic 'or' gate or logic 'nor' gate and has the advantages of that rising speeds are fast, logic levels are uniform, weak light can control strong light, and the like.

Optical logic gate device based on coherent feedback

The invention discloses an optical logic gate device on the basis of coherent feedback, which comprises a laser, polarization beam splitters, a medium unit, logic control gates, an optical fiber coupling frame and a multimode optical fiber. Pump light emitted by the laser enters a first polarization beam splitter and is reflected to the medium unit; after the pump light is subjected to four-wave mixing in the medium unit, an output light beam is generated and is emitted by a second polarization beam splitter to form a ring-shaped light spot and two bright spots in the vertical direction; two beams of feedback light are generated from the bright spots by a third polarization beam splitter; and the feedback light is controlled by a first logic control gate and a second logic control gate, enters the first polarization beam splitter by the optical fiber coupling frame and the multimode optical fiber and is crossed with the pump light in the medium unit. According to the invention, an optical logic OR gate and an optical logic NOR gate can be simultaneously implemented; and the optical logic gate device has the advantages of high ascending speed, consistent logic level, capability of controlling strong light by weak light and the like. The invention also discloses a working method of the optical logic gate device on the basis of coherent feedback.

Jun Zhou

Papers

Compact diode-laser-pumped quantum light source based on four-wave mixing in hot rubidium vapor

Optical logic gates using coherent feedback

Ultralow-light-level all-optical transistor in rubidium vapor

Optical logic gate device based on coherent feedback

Optical logic gate device on basis of coherent feedback and working method thereof