We present two experiments testing the hypothesis of noncontextual hidden variables (NCHV's). The first one is based on observation of two-photon pseudo-Greenberger-Horne-Zeilinger correlations, with two of the originally three particles mimicked by the polarization degree of freedom and the spatial degree of freedom of a single photon. The second one, a single-photon experiment, utilizes the same trick to emulate two particle correlations, and is an "event ready" test of a Bell-like inequality, derived from the noncontextuality assumption. Modulo fair sampling, the data falsify NCHV's.The statistical nature of quantum predictions has frequently initiated efforts to expand the quantum mechanical description. The so-called hidden variable concepts try to cure the quantum indeterminism by ascribing values to the properties of a system which are defined already prior to the measurement. The question arises whether such expansion of the theory is justified.noncontextual hidden variable (NCHV) theories assume that the predetermined result of a particular measurement does not depend on what other observable is simultaneously measured (see e.g. [1]). Such cryptodeterminism was ruled out by the Bell-Kochen-Specker (BKS) theorem [2], which, as a mathematical theorem, does not need experimental confirmation -and neither suggests one. Yet, quite recently, doubts arose about the usefullness of the BKS theorem due to the impossibility of experimentally testing the yes/no contradiction of the BKS theorem in real world, where one is always confined to finite measurement times and precision [3]. NCHV theories form a subset of local realistic hidden variable (LHV) theories, which rely on the more plausible assumption that the predetermined result of a particular measurement does not depend on what other observable is simultaneously measured in a spatially separated region. Bell's theorem [4] gives a clear prescription for a statistical test of LHV theories. However, almost all experiments testing LHV theories do not enforce spacelike separation of measurements, and all are plagued with the low detection efficiency, thus falling short of definitely invalidating LHV theories [5].We report two experiments testing the validity of NCHV theories. The experiments are much simpler than equivalent Bell tests (with no strict imposition of locality), and much less sensitive to experimental imperfections. This includes lower threshold interference visibility and consequently also less demanding threshold for detection efficiencies. The possible adaptation to other quantum systems paves the way to a loophole-free test of the particular class of noncontextual hidden variable theories. Formally, the experiments are employing the fact, that measurements on distinct tensor product factors of Hilbert space commute and can therefore form varying contexts for one another. In the analysis of these experiments we obtain, for a specific state [6], verifiable, statistical conditions for the measurement results. In the first experiment the three particl...
We present the experimental demonstration of a Bell-state analyzer employing two-photon interference effects. Photon pairs produced by parametric down-conversion allowed us to generate momentum-entangled Bell states and to demonstrate the properties of this device. The performance obtained indicates its readiness for use with quantum communication schemes and in experiments on the foundations of quantum mechanics.
We present a method for the selective etching of borosilicate glass (SCHOTT Borofloat 33), in which we modify the glass with an ultrashort pulse laser and subsequent wet chemical etching. The BF33 glass is often used in microtechnology to produce sensors, actors, and fluidic chips as it can be bonded to silicon wafers by anodic bonding. The glass is irradiated and modified by circular polarized laser light with a wavelength of 1030 nm. By etching the glass with potassium hydroxide, the modified material can be removed. In this study, the selectivity was analyzed dependent on the laser parameters pulse repetition rate, pulse duration, writing speeds, and pulse energy. A selectivity up to 540 could be observed in this study. Finally, the manufacturing capabilities for three-dimensional free form shapes in BF33 are demonstrated and compared with fused silica.
Quantum teleportation uses prior entanglement and forward classical communication to transmit one instance of an unknown quantum state. Remote state preparation (RSP) has the same goal, but the sender knows classically what state is to be transmitted. We show that the asymptotic classical communication cost of RSP is one bit per qubit-half that of teleportation-and even less when transmitting part of a known entangled state. We explore the tradeoff between entanglement and classical communication required for RSP, and discuss RSP capacities of general quantum channels. A principal goal of quantum information theory is understanding the resources necessary and sufficient for intact transmission of quantum states. In quantum telepor-tation [1] an unknown state is transmitted from a sender ("Alice") to a receiver ("Bob") using classical communication and prior entanglement. Two bits of forward classical communication and one ebit of entanglement (a maximally entangled pair of qubits) per teleported qubit are both necessary and sufficient, and neither resource can be traded off against the other. In remote state preparation (RSP) the goal is the same-for Bob to end up with a single specimen of a state-but here Al-ice starts with complete classical knowledge of the state. Pati [2] and Lo [3] showed that for special ensembles of states (e.g. qubit states on the equator of the Bloch sphere) RSP requires less classical communication than teleportation, but Lo conjectured that for general states the classical communication costs of the two tasks would be equal. Here we show that, in the presence of a large amount of prior entanglement, the asymptotic classical communication cost of RSP for general states is one bit per qubit, half that of teleportation. Most of this en-tanglement is not destroyed, but, as we will show, can be recovered afterward using backward classical communication from Bob to Alice, a resource that is entirely unhelpful for teleportation. We show that RSP is unlike teleportation in that it exhibits a nontrivial tradeoff between classical communication and entanglement, the classical cost of preparing a generic qubit state ranging from one bit in the high entanglement limit to infinitely many without prior en-tanglement (if any finite classical message, say of k bits, sufficed, Bob could use that message to make infinitely many copies, determine the state's amplitudes to more than k bits precision, and thereby violate causality). We introduce two new kinds of channel capacity, reflecting a general quantum channel's asymptotic ability to be used for remote state preparation, with or without prior entanglement, and relate these capacities to the regular quantum and classical capacities with or without prior entanglement. Finally, we discuss remote preparation of states entangled between Alice and Bob. RSP in the high-entanglement limit: To see how a large amount of shared entanglement enables general states to be remotely prepared at an asymptotic cost of one bit per qubit, it is helpful first to conside...
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