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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/1901.11004
    Experimental quantum teleportation
    Quantum teleportation -- the transmission and reconstruction over arbitrary distances of the state of a quantum system -- is demonstrated experimentally. During teleportation, an initial photon which carries the polarization that is to be transferred and one of a pair of entangled photons are subjected to a measurement such that the second photon of the entangled pair acquires the polarization of the initial photon. This latter photon can be arbitrarily far away from the initial one. Quantum teleportation will be a critical ingredient for quantum computation networks.
    ARXIV.ORG
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/2212.07502
    Entanglement measures for two-particle quantum histories
    Quantum entanglement is a key resource, which grants quantum systems the ability to accomplish tasks that are classically impossible. Here, we apply Feynman's sum-over-histories formalism to interacting bipartite quantum systems and introduce entanglement measures for bipartite quantum histories. Based on the Schmidt decomposition of the matrix comprised of the Feynman propagator complex coefficients, we prove that bipartite quantum histories are entangled if and only if the Schmidt rank of this matrix is larger than 1. The proposed approach highlights the utility of using a separable basis for constructing the bipartite quantum histories and allows for quantification of their entanglement from the complete set of experimentally measured sequential weak values. We then illustrate the non-classical nature of entangled histories with the use of Hardy's overlapping interferometers and explain why local hidden variable theories are unable to correctly reproduce all observable quantum outcomes. Our theoretical results elucidate how the composite tensor product structure of multipartite quantum systems is naturally extended across time and clarify the difference between quantum histories viewed as projection operators in the history Hilbert space or viewed as chain operators and propagators in the standard Hilbert space.
    ARXIV.ORG
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/quant-ph/0509060
    Noise thresholds for optical quantum computers
    In this paper we numerically investigate the fault-tolerant threshold for optical cluster-state quantum computing. We allow both photon loss noise and depolarizing noise (as a general proxy for all local noise), and obtain a threshold region of allowed pairs of values for the two types of noise. Roughly speaking, our results show that scalable optical quantum computing is possible for photon loss probabilities less than 0.003, and for depolarization probabilities less than 0.0001.
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/1906.01645
    Advances in Quantum Cryptography
    Quantum cryptography is arguably the fastest growing area in quantum information science. Novel theoretical protocols are designed on a regular basis, security proofs are constantly improving, and experiments are gradually moving from proof-of-principle lab demonstrations to in-field implementations and technological prototypes. In this review, we provide both a general introduction and a state of the art description of the recent advances in the field, both theoretically and experimentally. We start by reviewing protocols of quantum key distribution based on discrete variable systems. Next we consider aspects of device independence, satellite challenges, and high rate protocols based on continuous variable systems. We will then discuss the ultimate limits of point-to-point private communications and how quantum repeaters and networks may overcome these restrictions. Finally, we will discuss some aspects of quantum cryptography beyond standard quantum key distribution, including quantum data locking and quantum digital signatures.
    ARXIV.ORG
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  • Harvard University
    2025-02-07 00:00:00 -
    https://ui.adsabs.harvard.edu/abs/1928RSPSA.117..610D
    The Quantum Theory of the Electron
    Special relativistic formulation of Quantum mechanics
    UI.ADSABS.HARVARD.EDU
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/quant-ph/9703041
    Entanglement of a Pair of Quantum Bits
    The ``entanglement of formation'' of a mixed state of a bipartite quantum system can be defined in terms of the number of pure singlets needed to create the state with no further transfer of quantum information. We find an exact formula for the entanglement of formation for all mixed states of two qubits having no more than two non-zero eigenvalues, and we report evidence suggesting that the formula is valid for all states of this system.
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  • Harvard University
    2025-02-07 15:08:45 -
    https://ui.adsabs.harvard.edu/abs/2012Natur.483..439A
    Resonant quantum transitions in trapped antihydrogen atoms
    The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.
    UI.ADSABS.HARVARD.EDU
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/quant-ph/0102094
    The Role of Relative Entropy in Quantum Information Theory
    Quantum mechanics and information theory are among the most important scientific discoveries of the last century. Although these two areas initially developed separately it has emerged that they are in fact intimately related. In this review I will show how quantum information theory extends traditional information theory by exploring the limits imposed by quantum, rather than classical mechanics on information storage and transmission. The derivation of many key results uniquely differentiates this review from the "usual" presentation in that they are shown to follow logically from one crucial property of relative entropy. Within the review optimal bounds on the speed-up that quantum computers can achieve over their classical counter-parts are outlined using information theoretic arguments. In addition important implications of quantum information theory to thermodynamics and quantum measurement are intermittently discussed. A number of simple examples and derivations including quantum super-dense coding, quantum teleportation, Deutsch's and Grover's algorithms are also included.
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/1712.00706
    Indistinguishability of elementary systems as resource for quantum information processing
    Typical elements of quantum networks are made by identical systems, which are the basic particles constituting a resource for quantum information processing. Whether the indistinguishability due to particle identity is an exploitable quantum resource remains an open issue. Here we study independently prepared identical particles showing that, when they spatially overlap, an operational entanglement exists which can be made manifest by means of separated localized measurements. We prove this entanglement is physical in that it can be directly exploited to activate quantum information protocols, such as teleportation. These results establish that particle indistinguishability is a utilizable quantum feature and open the way to new quantum-enhanced applications.
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  • arxiv.org
    2024-08-17 00:00:00 -
    https://arxiv.org/abs/1305.5941
    Computing quantum discord is NP-complete
    We study the computational complexity of quantum discord (a measure of quantum correlation beyond entanglement), and prove that computing quantum discord is NP-complete. Therefore, quantum discord is computationally intractable: the running time of any algorithm for computing quantum discord is believed to grow exponentially with the dimension of the Hilbert space so that computing quantum discord in a quantum system of moderate size is not possible in practice. As by-products, some entanglement measures (namely entanglement cost, entanglement of formation, relative entropy of entanglement, squashed entanglement, classical squashed entanglement, conditional entanglement of mutual information, and broadcast regularization of mutual information) and constrained Holevo capacity are NP-hard/NP-complete to compute. These complexity-theoretic results are directly applicable in common randomness distillation, quantum state merging, entanglement distillation, superdense coding, and quantum teleportation; they may offer significant insights into quantum information processing. Moreover, we prove the NP-completeness of two typical problems: linear optimization over classical states and detecting classical states in a convex set, providing evidence that working with classical states is generically computationally intractable.
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  • ChatGPT AI
    2023-03-22 10:30:59 -



    Quantum computing is a form of computing that utilizes quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data. It is different from traditional computing in that it uses qubits instead of bits as its fundamental unit of information. This allows quantum computers to process data in ways that are not possible with classical computers, such as performing calculations much faster or solving certain problems that are intractable for classical computers. Quantum computing has the potential to revolutionize the way we solve problems and could lead to breakthroughs in fields such as artificial intelligence, cryptography, and materials science.

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  • ChatGPT AI
    2023-04-05 04:53:37 -



    The spin quantum number (s) is a quantum number associated with the angular momentum of a particle. It is related to the intrinsic angular momentum of a particle, and determines the energy levels and allowed transitions of the particle. The spin quantum number can be either +1/2 or -1/2, depending on the type of particle.

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  • ChatGPT AI
    2023-04-25 11:56:32 -



    Quantum information is the use of quantum mechanical phenomena such as entanglement and superposition to process information. It is an emerging interdisciplinary field that combines physics, computer science, mathematics, and engineering. It has applications in many areas of science and technology, including cryptography, computing, communication, and sensing. Quantum information is based on the principles of quantum mechanics, which describe how particles interact with each other at a subatomic level. In particular, quantum entanglement allows two or more particles to be linked together in such a way that they share the same quantum state. This allows for the transmission of information with greater security and efficiency than traditional methods.

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  • ChatGPT AI
    2023-06-05 13:02:31 -

    By: ChatGPT AI
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