Time-bin encoding is a robust form of optical quantum information, especially for transmission in optical fibers. To read out the information, the separation of the time bins must be larger than the detector time resolution, typically on the order of nanoseconds for photon counters. In the present work, we demonstrate a technique using a nonlinear interaction between chirped entangled time-bin photons and shaped laser pulses to perform projective measurements on arbitrary time-bin states with picosecond-scale separations. We demonstrate a tomographically-complete set of time-bin qubit projective measurements and show the fidelity of operations is sufficiently high to violate the CHSH-Bell inequality by more than 6 standard deviations.
Time-bin qudits have emerged as a promising encoding platform in many quantum photonic applications. However, the requirement for efficient single-shot measurement of time-bin qudits instead of reconstructive detection has restricted their widespread use in experiments. Here, we propose an efficient method to measure arbitrary superposition states of time-bin qudits and confirm it up to dimension 4. This method is based on encoding time bins at the picosecond time scale, also known as ultrafast time bins. By doing so, we enable the use of robust and phase-stable single spatial mode temporal in…
The photonic temporal degree of freedom is one of the most promising platforms for quantum communication over fiber networks and free-space channels. In particular, time-bin states of photons are robust to environmental disturbances, support high-rate communication, and can be used in high-dimensional schemes. However, the detection of photonic time-bin states remains a challenging task, particularly for the case of photons that are in a superposition of different time-bins. Here, we experimentally demonstrate the feasibility of picosecond time-bin states of light, known as ultrafast time-bins…
Quantum optical synthesis of high-dimensional ultrafast frequency-bin qudits
Graduate School of Informatics and Engineering, The University of Electro-Communications（电子通信大学信息工程研究生院）；Advanced ICT Research Institute, National Institute of Information and Communications Technology（国家信息通信技术研究所先进ICT研究所）；Institute for Advanced Science, The University of Electro-Communications（电子通信大学高等科学研究院）
Gaussian Boson Sampling (GBS) is a quantum computing concept based on drawing samples from a multimode nonclassical Gaussian state using photon-number resolving detectors. It was initially posed as a near-term approach aiming to achieve quantum advantage, but several applications have been proposed ever since, such as the calculation of graph features or molecular vibronic spectra, among others. For the first time, we use a time-bin encoded interferometer to implement GBS experimentally and extract samples to enhance the search for dense subgraphs in a graph. Our results indicate an improvemen…
Despite its widespread use in fiber optics, encoding quantum information in photonic time-bin states is usually considered impractical for free-space quantum communication as turbulence-induced spatial distortion impedes the analysis of time-bin states at the receiver. Here, we demonstrate quantum key distribution using time-bin photonic states distorted by turbulence and depolarization during free-space transmission. Utilizing a novel analyzer apparatus, we observe stable quantum bit error ratios of 5.32 %, suitable for generating secure keys, despite significant wavefront distortions and pol…
Free-space time-bin encoded quantum key distribution from near- to mid-infrared wavelengths
QTI s.r.l.（QTI有限公司）；CNR - Istituto Nazionale di Ottica (CNR-INO)（意大利国家研究委员会光学研究所）；LENS - European Laboratory for Non-Linear Spectroscopy（欧洲非线性光谱学实验室）；Università degli Studi di Firenze（佛罗伦萨大学）
A single photon has many physical degrees of freedom (DOF) that can carry the state of a high-dimensional quantum system. Nevertheless, only a single DOF is usually used in any specific demonstration. Furthermore, when more DOF are being used, they are analyzed and measured one at a time. We introduce a two-qubit information system, realized by two degrees of freedom of a single photon: polarization and time. The photon arrival time is divided into two time-bins representing a qubit, while its polarization state represents a second qubit. The time difference between the two time-bins is create…
Generation of frequency-bin-encoded dual-rail cluster states via time-frequency multiplexing of microwave photonic qubits
RIKEN Center for Quantum Computing (RQC)（理化学研究所量子计算中心）；Department of Applied Physics, Graduate School of Engineering, The University of Tokyo（东京大学大学院工学系研究科应用物理系）；Department of Applied Physics, Stanford University（斯坦福大学应用物理系）
Robust implementation of quantum key distribution requires precise state generation and measurements, as well as a transmission that is resistant to channel disturbances. However, the choice of the optimal encoding scheme is not trivial and depends on external factors such as the quantum channel. In fact, stable and low-error encoders are available for polarization encoding, suitable for free-space channels, whereas time-bin encoding represent a good candidate for fiber-optic channels, as birefingence does not perturb this kind of states. Here we present a cross-encoded scheme where high accur…
Unraveling real-time chemical shifts in the ultrafast regime
European XFEL（欧洲X射线自由电子激光实验室）；Departamento de Química, Universidad Autónoma de Madrid（马德里自治大学化学系）；Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid（马德里自治大学凝聚态物理中心（IFIMAC））；Instituto de Ciencia de Materiales (ICMM-CSIC)（材料科学研究所（ICMM-CSIC））；Laboratory for Ultrafast X-ray Sciences, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院化学科学与工程学院超快X射线科学实验室）；Laboratory of Theoretical Physical Chemistry, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院化学科学与工程学院理论物理化学实验室）；Department of Physics, Blackett Laboratory, Imperial College London（伦敦帝国理工学院布莱克特物理系）；Paul-Scherrer Institute（保罗谢尔研究所）；Institut für Experimentalphysik, Universität Hamburg（汉堡大学实验物理研究所）
Enforcing IID structure on time-bin encoded QKD protocols via coarse-graining
University of Waterloo（滑铁卢大学）；Institute for Quantum Computing（量子计算研究所）；Department of Physics and Astronomy, University of Waterloo（滑铁卢大学物理与天文系）；Cheriton School of Computer Science, University of Waterloo（滑铁卢大学切里顿计算机科学学院）；New York University Shanghai（纽约大学上海分校）
Heralding techniques are useful in quantum communication to circumvent losses without resorting to error correction schemes or quantum repeaters. Such techniques are realized, for example, by monitoring for photon loss at the receiving end of the quantum link while not disturbing the transmitted quantum state. We describe and experimentally benchmark a scheme that incorporates error detection in a quantum channel connecting two transmon qubits using traveling microwave photons. This is achieved by encoding the quantum information as a time-bin superposition of a single photon, which simultaneo…
Gigahertz-rate thin-film lithium niobate receiver for time-bin quantum communication
Università di Pavia（帕维亚大学）；Advanced Fiber Resources Milan s.r.l.（米兰先进光纤资源有限公司）；Università degli Studi di Padova（帕多瓦大学）；CEA LETI and University Grenoble Alpes（CEA-LETI和格勒诺布尔阿尔卑斯大学）
Squeezed states are a versatile class of quantum states with applications ranging from quantum computing to high-precision detection. We propose a method for generating tunable squeezed states of light with multiple modes encoded in frequency bins. Our method uses custom-engineered spontaneous parametric downconversion pumped by a pulse-shaped pump field. The multi-mode squeezed states are generated in a single pass and can be tuned in real time by adjusting the properties of the pump field. Exploring new quantum states of light, encoded in new degrees of freedom, can be a fruitful path toward…
Time-bin qubits, in which quantum information is encoded in a single photon at different times $Δ$t, are suitable for long-distance transmission via optical fibers. However, detection of time-bin qubits has been limited to the nanosecond range owing to the limited temporal resolution of single-photon detectors. In this study, we developed an up-conversion single-photon detector (UCSPD), using commercial nonlinear crystals of different lengths. By changing the crystal length and pump power, we quantitatively evaluated the efficiency and temporal resolution of the UCSPD and determined the optima…
Time-bin qubits, where information is encoded in a single photon at different times, have been widely used in optical fiber and waveguide based quantum communications. With the recent developments in distributed quantum computation, it is logical to ask whether time-bin encoded qubits may be useful in that context. We have recently realized a time-bin qubit controlled-phase (C-Phase) gate using a 2 X 2 optical switch based on a lithium niobate waveguide, with which we demonstrated the generation of an entangled state. However, the experiment was performed with only a pair of input states, and …
Teleportation is a fundamental concept of quantum mechanics with an important application in extending the range of quantum communication channels via quantum relay nodes. To be compatible with real-world technology such as secure quantum key distribution over fibre networks, such a relay node must operate at GHz clock rates and accept time-bin encoded qubits in the low-loss telecom band around 1550 nm. Here, we show that InAs/InP droplet epitaxy quantum dots with their sub-Poissonian emission near 1550 nm are ideally suited for the realisation of this technology. To create the necessary on-de…
We propose a scheme for the generation of hybrid states entangling a single-photon time-bin qubit with a coherent-state qubit encoded on phases. Compared to other reported solutions, time-bin encoding makes hybrid entanglement particularly well adapted to applications involving long-distance propagation in optical fibers. This makes our proposal a promising resource for future out-of-the-laboratory quantum communication. In this perspective, we analyze our scheme by taking into account realistic experimental resources and discuss the impact of their imperfections on the quality of the obtained…
