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Unconventional Rydberg pumping and applications in quantum information processing
摘要： We propose a mechanism of unconventional Rydberg pumping (URP) via simultaneously driving each Rydberg atom by two classical fields with different strengths of Rabi frequencies. This mechanism differs from the general Rydberg blockade or Rydberg antiblockade since it is closely related to the ground states of atoms, i.e., two atoms in the same ground state are stable while two atoms in different ground states are resonantly excited. Furthermore, we find the URP can be employed to simplify some special quantum information processing tasks, such as implementation of a three-qubit controlled-PHASE gate with only a single Rabi oscillation, preparation of two- and three-dimensional steady-state entanglement with two identical atoms, and realization of the autonomous quantum error correction in a Rydberg-atom-cavity system. The feasibility of the above applications is discussed explicitly by the state-of-the-art technology.
关键词： quantum error correction,Rydberg blockade,Unconventional Rydberg pumping,quantum information processing,Rydberg antiblockade,entanglement
更新于2025-09-23 15:23:52
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Direct characterization of linear and quadratically nonlinear optical systems
摘要： A central task in quantum-information processing is to characterize quantum processes. In the realm of optical quantum-information processing, this amounts to characterizing the transformations of the mode creation and annihilation operators. This transformation is unitary for linear optical systems, whereas these yield the well-known Bogoliubov transformations for systems with Hamiltonians that are quadratic in the mode operators. In this paper, we propose a shot-noise limited scheme for characterizing both these kinds of evolutions by employing a modified Mach-Zehnder interferometer. In order to characterize a N -mode device, we require O(N 2) measurements. Although it suffices to use coherent states for the characterization of linear optical systems, we additionally require single photons to characterize quadratically nonlinear optical systems.
关键词： Bogoliubov transformations,Mach-Zehnder interferometer,optical systems,quantum-information processing,coherent states,single photons
更新于2025-09-23 15:21:21
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Geometrical self-testing of partially entangled two-qubit states
摘要： Quantum nonlocality has recently been intensively studied in connection to device-independent quantum information processing, where the extremal points of the set of quantum correlations play a crucial role through self-testing. In most protocols, the proofs for self-testing rely on the maximal violation of the Bell inequalities, but there is another known proof based on the geometry of state vectors to self-test a maximally entangled state. We present a geometrical proof in the case of partially entangled states. We show that, when a set of correlators in the simplest Bell scenario satisfies a condition, the geometry of the state vectors is uniquely determined. The realization becomes self-testable when another unitary observable exists on the geometry. Applying this proven fact, we propose self-testing protocols by intentionally adding one more measurement. This geometrical scheme for self-testing is superior in that, by using this as a building block and repeatedly adding measurements, a realization with an arbitrary number of measurements can be self-tested. Besides the application, we also attempt to describe nonlocal correlations by guessing probabilities of distant measurement outcomes. In this description, the quantum set is also convex, and a large class of extremal points is identified by the uniqueness of the geometry.
关键词： device-independent quantum information processing,Bell inequality,quantum nonlocality,self-testing
更新于2025-09-23 15:21:01
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Adaptive tomography of qubits: purity versus statistical fluctuations
摘要： The success of quantum information processing applications relies on accurate and efficient characterization of quantum states, especially nearly-pure states. In this work, we investigate a procedure for adaptive qubit state tomography which achieves O(1/N) scaling in accuracy for large N. We analyze the performance of the adaptive protocol on the characterization of pure, mixed and nearly-pure states, and clarify the interplay between the purity of the state and the statistical fluctuations of the measurement results. Our results highlight the subtle difference between the characterization of nearly-pure states and those of pure or highly mixed states.
关键词： quantum information processing,quantum measurement,quantum tomography
更新于2025-09-23 15:19:57
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High Quality Entangled Photon Pair Generation in Periodically Poled Thin-Film Lithium Niobate Waveguides
摘要： A thin-film periodically poled lithium niobate waveguide was designed and fabricated which generates entangled photon pairs at telecommunications wavelengths with high coincidences-to-accidentals counts ratio CAR > 67000, two-photon interference visibility V > 99%, and heralded single-photon autocorrelation g(0) < 0.025. Nondestructive in situ diagnostics were used to determine the poling quality in 3D. Megahertz rates of photon pairs were generated by less than a milliwatt of pump power, simplifying the pump requirements and dissipation compared to traditional spontaneous parametric down-conversion lithium niobate devices.
关键词： lithium niobate waveguides,quantum information processing,entangled photon pairs,telecommunications wavelengths
更新于2025-09-23 15:19:57
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Long-distance entangling gates between quantum dot spins mediated by a superconducting resonator
摘要： Recent experiments with silicon qubits demonstrated strong coupling of a microwave resonator to the spin of a single electron in a double quantum dot, opening up the possibility of long-range spin-spin interactions. We present our theoretical calculation of effective interactions between distant quantum dot spins coupled by a resonator, and propose a protocol for fast, high-fidelity two-qubit gates consistent with experimentally demonstrated capabilities. Our simulations show that, in the presence of noise, spin-spin entangling gates significantly outperform cavity-mediated gates on charge qubits.
关键词： superconducting resonator,entangling gates,quantum dot spins,quantum information processing
更新于2025-09-19 17:13:59
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Phononic-waveguide-assisted steady-state entanglement of silicon-vacancy centers
摘要： Multiparticle entanglement is of great significance for quantum metrology and quantum information processing. We present here an efficient scheme for generating stable multiparticle entanglement in a solid-state setup, where an array of silicon-vacancy centers are embedded in a quasi-one-dimensional acoustic diamond waveguide. In this scheme, the continuum of phonon modes induces a controllable dissipative coupling among the SiV centers. We show that, by an appropriate choice of the distance between the SiV centers, the dipole-dipole interactions can be switched off due to destructive interference, thus realizing a Dicke superradiance model. This gives rise to an entangled steady state of SiV centers with high fidelities. The protocol provides a feasible setup for the generation of multiparticle entanglement in a solid-state system.
关键词： Multiparticle entanglement,quantum information processing,acoustic diamond waveguide,quantum metrology,silicon-vacancy centers,Dicke superradiance model
更新于2025-09-19 17:13:59
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Continuous-wave 6-dB-squeezed light with 2.5-THz-bandwidth from single-mode PPLN waveguide
摘要： Terahertz (THz)-bandwidth continuous-wave (CW) squeezed light is essential for integrating quantum processors with time-domain multiplexing (TDM) by using optical delay line interferometers. Here, we utilize a single-pass optical parametric amplifier (OPA) based on a single-spatial-mode periodically poled ZnO:LiNbO3 waveguide, which is directly bonded onto a LiTaO3 substrate. The single-pass OPA allows THz bandwidth, and the absence of higher-order spatial modes in the single-spatial-mode structure helps avoid degradation of squeezing. In addition, the directly bonded ZnO-doped waveguide has durability for high-power pump and shows small photorefractive damage. Using this waveguide, we observe CW 6.3-dB squeezing at 20-MHz sideband by balanced homodyne detection. This is the first realization of CW squeezing with a single-pass OPA at a level exceeding 4.5 dB, which is required for the generation of a two-dimensional cluster state. Furthermore, the squeezed light shows 2.5-THz spectral bandwidth. The squeezed light will lead to the development of a high-speed on-chip quantum processor using TDM with a centimeter-order optical delay line.
关键词： terahertz-bandwidth,quantum information processing,squeezed light,continuous-wave,single-mode PPLN waveguide
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Frequency-Multiplexed Singly-Resonant Photon Pairs from a Quadratic Nonlinear Waveguide Resonator
摘要： Frequency multiplexed photon pair generation has been actively studied for efficient and large-scale photonic quantum information processing [1-3]. In these demonstrations, photon pair generators were realized by using an optical parametric oscillator (OPO) far below threshold; a nonlinear optical medium was inside or integrated with an optical cavity, and a sufficiently weak pump light for the photon pair generation was used. However, to the best of our knowledge, all of the previous demonstrations for frequency multiplexed photon pair generation have used a doubly-resonant OPO which confines both the signal and the idler photons, or a triply-resonant OPO which additionally confines the pump light. In this study, we demonstrate a frequency multiplexed photon pair generation based on a singly-resonant (SR) OPO configuration which confines only one half of the photon pair. We used a periodically-poled lithium niobate (PPLN) waveguide as a monolithically-integrated quadratic nonlinear waveguide resonator; dielectric multilayers are directly formed at the end faces of the PPLN waveguide such that only the signal photon around 1600 nm of the photon pair is confined in the resonator and the idler photon around 1522 nm and the pump light at 780 nm are not confined. In the SR photon pair, in spite of no cavity configuration for the idler photons, not only the signal photons but also the idler photons have comb-like spectra as if both of them are confined in the cavity. In addition, there is not missing teeth region observed in multiple resonant OPO configuration known as the cluster effect [4,5]. As a result, a wide-band frequency multiplexed photon pair generation can be possible. The photon pair generator will be useful for an efficient photonic quantum information processing and a frequency-domain photon manipulation with the use of frequency-domain optical elements [6-9].
关键词： singly-resonant OPO,PPLN waveguide,photon pair generation,quantum information processing,frequency multiplexed
更新于2025-09-16 10:30:52
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Distinctive characteristics of carrier-phonon interactions in optically driven semiconductor quantum dots
摘要： We review distinct features arising from the unique nature of the carrier-phonon coupling in self-assembled semiconductor quantum dots. Because of the discrete electronic energy structure, the pure dephasing coupling usually dominates the phonon effects, of which two properties are of key importance: The resonant nature of the dot-phonon coupling, its non-monotonic behavior as a function of energy, and the fact that it is of super-Ohmic type. Phonons do not only act destructively in quantum dots by introducing dephasing, they also offer new opportunities, e.g. in state preparation protocols. Apart from being an interesting model systems for studying fundamental physical aspects, quantum dot and quantum dot-microcavity systems are a hotspot for many innovative applications. We discuss recent developments related to the decisive impact of phonons on key figures of merit of photonic devices like single or entangled photon sources under aspects like indistinguishability, purity and brightness. All in all it follows that understanding and controlling the carrier-phonon interaction in semiconductor quantum dots is vital for their usage in quantum information technology.
关键词： Non-Markovian dynamics,quantum information processing,optical manipulation,Semiconductor quantum dots,carrier-phonon interaction,photonics
更新于2025-09-12 10:27:22