We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in is exploited for two independent squeezed beams. These interfere at beam splitter and EPR obtained between output correlation amplitude (phase) quadratures measured to be 4.0+/-0.2 (4.0+/-0.4) dB below quantum noise limit. sum criterion these squeezing variances 0.80+/-0.03<2 verifies nonseparability state. product inferred...

A concept of polarization entanglement for continuous variables is introduced. For this purpose the Stokes-parameter operators and associated Poincar\'e sphere, which describe quantum-optical properties light, are defined their basic reviewed. The general features Stokes illustrated by evaluation means variances a range simple states. Some examples show squeezing, in one or more parameters smaller than coherent-state value. main object paper application these concepts to bright squeezed...

We suggest a quantum cryptographic scheme using continuous EPR-like correlations of bright optical beams. For binary key encoding, the information is discretized in novel way by associating respective measurement, amplitude, or phase, with bit value ``1'' ``0.'' The secure distribution guaranteed correlations. No predetermined sent through channel contributing to security system.

We experimentally demonstrate a protocol for entanglement distribution by separable quantum system. In our experiment, two spatially separated modes of an electromagnetic field get entangled local operations, classical communication, and transmission correlated but mode between them. This highlights the utility correlations beyond establishment fundamental information resource verifies that its dual communication is possible.

The QuVis Quantum Mechanics Visualization project aims to address challenges of quantum mechanics instruction through the development interactive simulations for learning and teaching mechanics. In this article, we describe evaluation focusing on two-level systems developed as part Institute Physics resources. Simulations are research-based have been iteratively refined using student feedback in individual observation sessions in-class trials. We give evidence that these helping students...

Digital signatures guarantee the authorship of electronic communications. Currently used ``classical'' signature schemes rely on unproven computational assumptions for security, while quantum only laws mechanics to sign a classical message. Previous have unambiguous measurements. Such measurements, however, sometimes give no result, reducing efficiency protocol. Here, we instead use heterodyne detection, which always gives although there is some uncertainty. We experimentally demonstrate...

In this review we discuss intriguing properties of apparently classical optical fields, that go beyond purely context and allow us to speak about quantum characteristics such fields their applications in technologies. We briefly define the genuinely concepts entanglement steering. then move boarder line between world introducing discord, a more general concept coherence, finally controversial notion entanglement. To unveil aspects often classically perceived systems, focus detail on...

Quantum correlations of photon numbers in different spectral components ultrashort optical solitons have been observed experimentally. These are crucial for the understanding and characterization internal quantum structure soliton pulses contribute significantly to squeezing by filtering. The accessible information on nonclassical state correlated is discussed with example two modes. method may be generalized obtain a complete description multimode field.

We study quantum correlations beyond entanglement in two-mode Gaussian states of continuous-variable systems by means the measurement-induced disturbance (MID) and its ameliorated version (AMID). In analogy with recent studies discord, we define a AMID constraining optimization to all bi-local positive operator valued measurements. solve explicitly for relevant families states, including squeezed thermal states. Remarkably, find that there is finite subset comprising pure where non-Gaussian...

We describe a collection of interactive animations and visualizations for teaching quantum mechanics. The can be used at all levels the undergraduate curriculum. Each animation includes step-by-step exploration that explains key points. instructor resources are freely available. By using diagnostic survey, we report substantial learning gains students who have worked with animations.

We formulate polarization uncertainty relations and squeezing criteria in a SU(2) invariant manner. In this formulation the coherent states are only minimum states. show that is nonclassical property. analyze relation between other properties such as entanglement quadrature squeezing.

We present a protocol for performing entanglement swapping with intense pulsed beams. In first step, the generation of amplitude correlations between two systems that have never interacted directly is demonstrated. This verified in direct detection electronic modulation detected photocurrents. The measured are better than expected from classical reconstruction scheme. an process, four-partite entangled state generated. prove experimentally amplitudes four optical modes quantum correlated 3...

We report on the generation of polarization squeezing intense, short light pulses using an asymmetric fiber Sagnac interferometer. The Kerr nonlinearity is exploited to produce independent amplitude squeezed pulses. properties spatially overlapped and coherent states are discussed. experimental results for a single beam compared case two phase-matched, For latter, noise variances -3.4dB below shot in S0 S1 -2.8dB S2 Stokes parameters were observed, which comparable input magnitude....

We study nonclassical correlations beyond entanglement in a family of two-mode non-Gaussian states which represent the continuous-variable counterpart two-qubit Werner states. evaluate quantum discord and other quantumness measures obtaining exact analytical results special instances, upper lower bounds general case. Non-Gaussian measurements such as photon counting are necessary to solve optimization definition discord, whereas Gaussian strictly suboptimal for considered The gap between...

Digital signatures ensure the integrity of a classical message and authenticity its sender. Despite their far-reaching use in modern communication, currently used signature schemes rely on computational assumptions will be rendered insecure by quantum computer. We present digital (QDS) scheme whose security is instead based impossibility perfectly deterministically distinguishing between states. Our continuous-variable (CV) relies phase measurement distributed alphabet coherent states allows...

Quantum state sharing (QSS) is a protocol by which (secret) quantum may be securely split into shares, shared between multiple potentially-dishonest players, and reconstructed. Crucially, the players are each assumed to dishonest, so QSS requires that only collaborating authorized subset of can access original secret state; any dishonest unauthorized conspiracy cannot reconstruct it. We analyze involving three untrusted demonstrate steering required resource enabling proceed securely. level...

Entangling two systems at distant locations using a separable mediating ancilla is counterintuitive phenomenon proposed for qubits by T. Cubitt et al. [Phys. Rev. Lett. 91, 037902 (2003)]. We show that such entanglement distribution possible with Gaussian states, certain three-mode fully mixed state and linear optics elements readily available in experiments. Two modes of the become entangled sequentially mixing them on beam splitters, while third one remains all stages protocol.

Agile cryptography allows for a resource-efficient swap of cryptographic core in case the security an underlying classical algorithm becomes compromised. Conversely, versatile user to switch task without requiring any knowledge its inner workings. In this paper, we suggest how these related principles can be applied field quantum by explicitly demonstrating two protocols, digital signatures (QDS) and secret sharing (QSS), on same hardware sender receiver platform. Crucially, protocols differ...

Abstract Quantum-communication needs a source of entanglement which is accessible to non-local measurements. It shown that an entangled pair light beams may be generated from two bright amplitude squeezed beams. This applicable pulses and optical solitons in fibres. A possible experimental scheme for stroboscopic quantum teleportation discussed.

The question of an efficient multimode description optical pulses is studied. We show that a relatively very small number nonmonochromatic modes can be sufficient for complete quantum with Gaussian quadrature statistics. For example, three-mode was enough to reproduce the experimental data photon correlations in solitons [S. Sp\"alter, N. Korolkova, F. K\"onig, A. Sizmann, and G. Leuchs, Phys. Rev. Lett. 81, 786 (1998)]. This approach useful detailed understanding squeezing properties...

We investigate the physical mechanism behind counterintuitive phenomenon, distribution of continuous-variable entanglement between two distant modes by sending a third separable auxiliary mode them. For this purpose, we propose more simple and efficient protocol resulting in distributed with than an order magnitude higher logarithmic negativity previously proposed protocol. This shows that originates from one used for distribution, which is first destroyed local correlated noises restored...

We present a setup for performing sub-shot-noise measurements of the phase quadrature intense pulsed light without use separate local oscillator. A Mach-Zehnder interferometer with an unbalanced arm length is used to detect fluctuations at single sideband frequency. With this setup, nonseparability pair quadrature-entangled beams demonstrated experimentally.