Generating Optical Schrödinger Kittens for Quantum Information Processing

Ourjoumtsev, Alexei; Tualle-Brouri, Rosa; Laurat, Julien; Grangier, Philippe

doi:10.1126/science.1122858

Cited by 846 publications

(865 citation statements)

References 27 publications

(26 reference statements)

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“…The most notable example is certainly their use for an optical quantum computer [10,11], alongside their employment for improving teleportation [12][13][14], cloning [15], and storage [16]. Several implementations of non-Gaussian states have been reported so far, in particular from squeezed light [17][18][19][20][21][22][23][24][25], close-tothreshold parametric oscillators [26,27] in optical cavities [28], and in superconducting circuits [29]. Non-Gaussian operations are also interesting for tasks such as entanglement distillation [30,31] and noiseless amplification [32,33], which are also obtained in a conditional fashion, accepting only those events heralded by a measurement result.…”

Section: Introduction and Definitionsmentioning

confidence: 99%

Non-Gaussianity of quantum states: An experimental test on single-photon-added coherent states

et al. 2010

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Non-Gaussian states and processes are useful resources in quantum information with continuous variables. An experimentally accessible criterion has been proposed to measure the degree of non-Gaussianity of quantum states based on the conditional entropy of the state with a Gaussian reference. Here we adopt such a criterion to characterize an important class of nonclassical states: single-photon-added coherent states. Our studies demonstrate the reliability and sensitivity of this measure and use it to quantify how detrimental is the role of experimental imperfections in our implementation.

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Section: Introduction and Definitionsmentioning

confidence: 99%

Non-Gaussianity of quantum states: An experimental test on single-photon-added coherent states

et al. 2010

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“…The reported entanglement distillation, purification and Gaussification protocol can be iterated 7,8 and combined with already experimentally demonstrated single-photon subtraction [24][25][26] , quantum memory 3 and entanglement swapping 13,14 to build a continuous-variable quantum repeater. Our experiment is thus an important enabling step towards truly long-distance quantum communication with continuous variables.…”

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confidence: 99%

“…Our protocol enhances the entanglement and purity of the decohered states and represents a single step of an iterative Gaussification scheme 7,8 that asymptotically converts any input state into a Gaussian one. Moreover, if combined with a single de-Gaussifying operation such as the recently demonstrated single-photon subtraction from squeezed beams [24][25][26] , it would provide a generic continuous-variable entanglement purification and distillation scheme 7,8 , that is capable, for instance, of suppressing the detrimental effect of losses in quantum state transmission.…”

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Preparation of distilled and purified continuous-variable entangled states

et al. 2008

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The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to decoherence and destroy the non-classical states after some finite transmission-line length. Quantum repeater protocols 1,2 , which combine quantum memory 3 , entanglement distillation 4,5 and entanglement swapping 6 , were proposed to overcome this problem. Here we report on the experimental demonstration of entanglement distillation in the continuous-variable regime 7-9 . Entangled states were first disturbed by random phase fluctuations and then distilled and purified using interference on beam splitters and homodyne detection. Measurements of covariance matrices clearly indicate a regained strength of entanglement and purity of the distilled states. In contrast to previous demonstrations of entanglement distillation in the complementary discrete-variable regime 10,11 , our scheme achieved the actual preparation of the distilled states, which might therefore be used to improve the quality of downstream applications such as quantum teleportation 12 .Quantum information makes use of the special properties of quantum states to improve the quality of communication and information processing tasks. Generally, a quantized field can be described by the number operator or alternatively by two non-commuting position and momentum-like operators. The corresponding measurement results have either discrete or continuous spectra and form the basis of discrete-variable or continuous-variable quantum information, respectively. In the regime of continuous variables, entangled states of light can be deterministically generated in optical parametric amplifiers (OPAs), precisely manipulated with linear optics and measured with very high efficiency in balanced homodyne detectors. These entangled two-mode squeezed states show Gaussian probability distributions and were used for quantum teleportation 12 and entanglement swapping 13,14 . Entangled states of the collective spins of two atomic ensembles analogous to two-mode squeezed states have been generated 15 , storage of quantum states of light in an atomic memory has been demonstrated 3 and teleportation from light onto an atomic ensemble has been reported 16 . High-speed quantum cryptography with coherent light beams and homodyne detection has been demonstrated 17 . All these spectacular achievements reveal the great potential of this approach to quantum information processing.A missing piece in this toolbox has been a feasible protocol for entanglement distillation and purification. Entanglement distillation 4,5 extracts from several shared copies of weakly entangled mixed states a single copy of a highly entangled state using only local quantum operations and classical communication between the two parties sharing the states. This turned out to be a very challenging task for continuous-variable states, because it was proved that it is impossible to distil Gaussian entangled states by ...

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“…If the photon that causes the click comes from crystal I, then it is subtracted from the single-mode squeezed state, producing a negative Schrödinger cat in the CV mode [13,14,22]. The DV mode is in the vacuum state in this case, because of the low degree of two-mode squeezing obtained from crystal II.…”

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“…where |cat ± denote, respectively, positive and negative "Schrödinger cat" states N ± (|α ± |−α ) [13][14][15] in the CV mode C and {|0 D , |1 D } is the Fock basis for DV mode D, with N ± = 1/ √ 2 ± 2e −2α 2 being the normalization factor. The CV part of the resource (1) is distributed to Alice, while the DV part goes to Bob.…”

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Quantum Teleportation Between Discrete and Continuous Encodings of an Optical Qubit

et al. 2017

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Transfer of quantum information between physical systems of a different nature is a central matter in quantum technologies. Particularly challenging is the transfer between discrete-and continuous degrees of freedom of various harmonic oscillator systems. Here we implement a protocol for teleporting a continuous-variable optical qubit, encoded by means of coherent states, onto a discretevariable, single-rail qubit -a superposition of the vacuum-and single-photon optical states -via a hybrid entangled resource. We test our protocol on coherent states of different phases and obtain the teleported qubit with a fidelity of 0.83 ± 0.04. We also find that the phase of the resulting qubit varies consistently with that of the input, having a standard deviation of 3.8 • from the target value. Our work opens up the way to wide application of quantum information processing techniques where discrete-and continuous-variable encodings are combined within the same optical circuit.Real-world application of quantum technologies in many cases requires simultaneous use of physical systems of a different nature [1] in the hybrid fashion. For example, one of the most promising platforms for quantum information processing is superconducting circuitry, best storage times are achieved in atomic systems, whereas transmission of that information in space is better realized with photons.Within quantum optics, the hybrid paradigm consists in symbiotic involvement of states and methods from discrete (DV) and continuous (CV) variable domains. Fortes of both can thereby be employed at once; for example, the continuous part takes advantage of the de- terministic state preparation and relatively simple integration with existing information technologies [2], while the discrete side benefits from a natural photodetection basis and "built-in" entanglement distillation after losses [3]. This flexibility allows hybrid quantum technologies to offer protocols which are superior to both pure CV and DV solutions [4]. For example, using hybrid methods in quantum computing [5] and error correction [6] is favorable, compared to the mainstream CV and DV protocols, in terms of the number of resources required. Long-distance distribution of CV entanglement requires hybrid processing to mitigate the effect of propagation losses [7,8].Taking advantage of these protocols however requires a procedure for transferring quantum data between continuous and discrete qubit systems [4,9]; hybrid teleportation is therefore identified as one of the three key priorities for quantum teleportation science [10]. In this work we make a step towards this goal, demonstrating quantum teleportation by means of a hybrid entangled channel. Specifically, we develop a technique to teleport a CV qubit, encoded as a superposition of coherent states, onto a DV qubit -a superposition of the vacuum and single-photon Fock states. The protocol is conceptually different from the teleportation of photonic bits by a hybrid technique [11], in which both the input and output states are discrete-...

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Generating Optical Schrödinger Kittens for Quantum Information Processing

Cited by 846 publications

References 27 publications

Non-Gaussianity of quantum states: An experimental test on single-photon-added coherent states

Non-Gaussianity of quantum states: An experimental test on single-photon-added coherent states

Preparation of distilled and purified continuous-variable entangled states

Quantum Teleportation Between Discrete and Continuous Encodings of an Optical Qubit

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