Experimental Realization of the Quantum Box Problem

The three-box problem is a gedankenexperiment designed to elucidate some interesting features of quantum measurement and locality. A particle is prepared in a particular superposition of three boxes, and later found in a different (but nonorthogonal) superposition. It was predicted that appropriate "weak" measurements of particle position in the interval between preparation and post-selection would find the particle in two different places, each with certainty. We verify these predictions in an optical experiment and address the issues of locality and of negative probability.Comment: 5 pages, 4 figure

Practical measurement of joint weak values and their connection to the annihilation operator

Weak measurements are a new tool for characterizing post-selected quantum systems during their evolution. Weak measurement was originally formulated in terms of von Neumann interactions which are practically available for only the simplest single-particle observables. In the present work, we extend and greatly simplify a recent, experimentally feasible, reformulation of weak measurement for multiparticle observables [Resch and Steinberg (2004, Phys. Rev. Lett., 92, 130402)]. We also show that the resulting ``joint weak values'' take on a particularly elegant form when expressed in terms of annihilation operators.Comment: 13 pages, accepted to Physics Letters A (Dec. 2004

Compact coupler designs for quantum optical circuits produced by direct UV writing

Integrated planar lightwave circuits (PLCs) provide a promising route to small-scale quantum optical networks [1]. Recent work on quantum logic gates using silica-based PLCs has highlighted the opportunities afforded by the ability to coherently manipulate degrees of freedom at the level of single photons [2]. Increasingly complex waveguide networks are required for linear optics quantum computing (LOQC), a route towards small scale quantum information processing [3]. This approach uses quantum interference between photons and measurements with feedforward to implement the nonlinear interactions between photons that are required for information processing. A major issue in developing such circuits is the internal loss and the coupling efficiency of input photon from optical fibers

Observing Dirac's classical phase space analog to the quantum state

In 1945, Dirac attempted to develop a "formal probability" distribution to describe quantum operators in terms of two noncommuting variables, such as position x and momentum p [Rev. Mod. Phys. 17, 195 (1945)]. The resulting quasiprobability distribution is a complete representation of the quantum state and can be observed directly in experiments. We measure Dirac's distribution for the quantum state of the transverse degree of freedom of a photon by weakly measuring transverse x so as to not randomize the subsequent p measurement. Furthermore, we show that the distribution has the classical-like feature that it transforms (e.g., propagates) according to Bayes' law. \ua9 2014 American Physical Society.Peer reviewed: YesNRC publication: Ye

On the fundamental role of dynamics in quantum physics

Quantum theory expresses the observable relations between physical properties in terms of probabilities that depend on the specific context described by the "state" of a system. However, the laws of physics that emerge at the macroscopic level are fully deterministic. Here, it is shown that the relation between quantum statistics and deterministic dynamics can be explained in terms of ergodic averages over complex valued probabilities, where the fundamental causality of motion is expressed by an action that appears as the phase of the complex probability multiplied with the fundamental constant hbar. Importantly, classical physics emerges as an approximation of this more fundamental theory of motion, indicating that the assumption of a classical reality described by differential geometry is merely an artefact of an extrapolation from the observation of macroscopic dynamics to a fictitious level of precision that does not exist within our actual experience of the world around us. It is therefore possible to completely replace the classical concepts of trajectories with the more fundamental concept of action phase probabilities as a universally valid description of the deterministic causality of motion that is observed in the physical world.Comment: More compact version set in RevTex (15 pages), overview of the paper added to the introduction, along with additional explanations of the relation between statistics and the action of deterministic transformations in section II. Final version for publication in The European Physical Journal

Derivation of the statistics of quantum measurements from the action of unitary dynamics

[[abstract]]Quantum statistics is defined by Hilbert space products between the eigenstates associated with state preparation and measurement. The same Hilbert space products also describe the dynamics generated by a Hamiltonian when one of the states is an eigenstate of energy E and the other represents an observable B . In this paper, we investigate this relation between the observable time evolution of quantum systems and the coherence of Hilbert space products in detail. It is shown that the times of arrival for a specific value of B observed with states that have finite energy uncertainties can be used to derive the Hilbert space product between eigenstates of energy E and eigenstates of the dynamical variable B . Quantum phases and interference effects appear in the form of an action that relates energy to time in the experimentally observable dynamics of localized states. We illustrate the relation between quantum coherence and dynamics by applying our analysis to several examples from quantum optics, demonstrating the possibility of explaining non-classical statistics in terms of the energy-time relations that characterize the corresponding transformation dynamics of quantum systems.[[notice]]補正完