Quantum information science has reinvigorated the study of quantum measurement, and created a new sense of urgency. I present several classes of ldquomeasurementrdquo and discuss their applications, their practical feasibility, and some outstanding theoretical issues.
While quantum measurement has long been seen as a deep philosophical conundrum, technological progress and new potential applications such as quantum information processing have turned it into a respectable experimental discipline as well. I will introduce a modern perspective on real-world quantum measurement, including the new paradigm of "weak measurement" and its (controversial) potential for addressing fundamental issues as well as for improving the precision of practical measurement.
Quantum non-locality has been an extremely fruitful subject of research, leading the scientific revolution towards quantum information science, in particular, to device-independent quantum information processing. We argue that the time is ripe to work on another basic problem in the foundations of quantum physics, the quantum measurement problem, which should produce good physics in theoretical, mathematical, experimental and applied physics. We briefly review how quantum non-locality contributed to physics (including some outstanding open problems) and suggest ways in which questions around macroscopic quantumness could equally contribute to all aspects of physics.This article is part of a discussion meeting issue 'Foundations of quantum mechanics and their impact on contemporary society'.
Cavity quantum optomechanics has emerged as a new platform for quantum science and technology and has applications ranging from quantum-information processing to tests of the foundations of physics. Of crucial importance for optomechanics is the generation and verification of non-Gaussian states of motion and a key outstanding challenge is the observation of a canonical two-mode Schrodinger-cat state in the displacement of two mechanical oscillators. In this work, we introduce a protocol that utilizes the nonlinearity of the radiation-pressure interaction combined with photon-counting measurements to generate this bipartite non-Gaussian mechanical state. Our protocol employs short optical pulses to both generate the mechanical quantum state, and to then measure arbitrary mechanical quadrature moments, which we utilize to verify the non-Gaussian entanglement. Our entanglement-verification procedure can be used to evaluate an entire class of inseparability criteria and also provides a route for experimental characterisation of a broad range of single- and multi-partite mechanical states. Key experimental factors, such as optical loss and mechanical decoherence, are carefully analyzed and we show that the scheme is feasible with only minor improvements to current experiments that operate outside the resolved-sideband regime. Our scheme provides a new avenue for quantum experiments with entangled mechanical oscillators and offers significant potential for further research and development that utilizes such non-Gaussian states for quantum-information and sensing applications, and for studying the quantum-to-classical transition.
This paper introduces the Quantum Measurement Feedback Loop (QMFL), a novel framework fundamentally shifting the paradigm of quantum measurement. Traditionally, quantum measurement is conceived as a unidirectional process, where a system is observed by an observer. The QMFL proposes a bidirectional interaction, establishing a closed-loop feedback system. This cyclical relationship, represented mathematically as [System↔Observer], allows for active influence of the observer on the system being measured, potentially leading to significant advancements in quantum measurement techniques and exploring new avenues for quantum information processing. The core concept leverages the inherent uncertainty within quantum measurement to create a dynamic interaction, offering a pathway to mitigate measurement disturbance and improve measurement fidelity. This work outlines the theoretical framework, presents a potential experimental setup utilizing a quantum measurement platform, and discusses the potential for this approach to yield breakthroughs in measurement science, with implications for applications ranging from quantum sensing to fundamental quantum theory. ---