Optical networks are the leading platform for the transfer of information due to their low loss and ability to scale to many information channels using optical frequency modes. To fully leverage the quantum properties of light in this platform, it is desired to manipulate higher-dimensional superpositions by orchestrating linear, beamsplitter-type interactions between several channels simultaneously. We propose a method of achieving simultaneous, all-to-all coupling between N optical frequency modes via N-way Bragg-scattering four-wave mixing. By exploiting the frequency degree of freedom, additional modes can be multiplexed in an interaction medium of fixed volume and loss, avoiding the introduction of excess noise. We generalize the theory of the frequency-encoded two-mode interaction to N modes under this four-wave mixing approach and experimentally verify the quantum nature of this scheme by demonstrating three-way multiphoton interference. The two input photons are shared among three frequency modes and display interference differing from that of two classical (coherent-state) inputs. These results show the potential of our approach for the scalability of photonic quantum information processing to general N-mode systems in the frequency domain.
Implementing spatially-encoded universal linear multiport interferometers on integrated photonic platforms with high controllability becomes increasingly difficult as the number of modes increases. In this work, we consider an architecture in which temporally-encoded modes are injected into a chain of reconfigurable beamsplitters and delay loops, and provide a detailed loss analysis for this and other comparable architectures. This analysis also yields a straightforward and explicit description of the control sequence needed for implementing an arbitrary temporally-encoded transformation. We c…
We report experimental realization of high-fidelity photonic quantum gates for frequency-encoded qubits and qutrits based on electro-optic modulation and Fourier-transform pulse shaping. Our frequency version of the Hadamard gate offers near-unity fidelity ($0.99998\pm0.00003$), requires only a single microwave drive tone for near-ideal performance, functions across the entire C-band (1530-1570 nm), and can operate concurrently on multiple qubits spaced as tightly as four frequency modes apart, with no observable degradation in the fidelity. For qutrits we implement a $3\times 3$ extension of …
A paradigm for universal quantum information processing with integrated acousto-optic frequency beamsplitters
Purdue University（普渡大学）；Oak Ridge National Laboratory（橡树岭国家实验室）；Northern Arizona University（北亚利桑那大学）；Sandia National Laboratories（桑迪亚国家实验室）；Qunnect Inc.（Qunnect公司）
Fourth-order interference is an information processing primitive for photonic quantum technologies. When used in conjunction with post-selection, it forms the basis of photonic controlled logic gates, entangling measurements, and can be used to produce quantum correlations. Here, using classical weak coherent states as inputs, we study fourth-order interference in novel $4 \times 4$ multi-port beam splitters built within multi-core optical fibers. Using two mutually incoherent weak laser pulses as inputs, we observe high-quality fourth order interference between photons from different cores, a…
Generalised quantum measurements go beyond the textbook concept of a projection onto an orthonormal basis in Hilbert space. They are not only of fundamental relevance but have also an important role in quantum information tasks. However, it is highly demanding to certify that a generalised measurement is indeed required to explain the results of a quantum experiment in which only the degrees of freedom are assumed to be known. Here, we use state-of-the-art multicore optical fiber technology to build multiport beamsplitters and faithfully implement a seven-outcome generalised measurement in a f…
We demonstrate a monolithic III-V photonic circuit combining a heralded single photon source with a beamsplitter, at room temperature and telecom wavelength. Pulsed parametric down-conversion in an AlGaAs waveguide generates counterpropagating photons, one of which is used to herald the injection of its twin into the beamsplitter. We use this configuration to implement an integrated Hanbury-Brown and Twiss experiment, yielding a heralded second-order correlation $g^{(2)}_{\rm her}(0)=0.10 \pm 0.02$ that confirms single-photon operation. The demonstrated generation and manipulation of quantum s…
In continuous-variable quantum computing with qubits encoded in the infinite-dimensional Hilbert space of bosonic modes, it is a difficult task to realize strong and on-demand interactions between the qubits. One option is to engineer a beamsplitter interaction for photons in two superconducting cavities by driving an intermediate superconducting circuit with two continuous-wave drives, as demonstrated in a recent experiment. Here, we show how quantum optimal control theory (OCT) can be used in a systematic way to improve the beamsplitter interaction between the two cavities. We find that repl…
The well-known Hong-Ou-Mandel effect is revisited. Two physical reasons are discussed for the effect to be less pronounced or even to disappear: differing polarizations of photons coming to the beamsplitter and delay time of photons in one of two channels. For the latter we use the concepts of biphoton frequency and temporal wave functions depending, correspondingly, on two frequency continuous variables of photons and on two time variables $t_1$ and $t_2$ interpreted as the arrival times of photons to the beamsplitter. Explicit expressions are found for the probability densities and total pro…
High-resolution tunable frequency beamsplitter enabled by an integrated silicon pulse shaper
Elmore Family School of Electrical and Computer Engineering and Purdue Quantum Science and Engineering Institute, Purdue University（普渡大学埃尔莫电气与计算机工程学院及普渡量子科学与工程研究所）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文学系）；Photonic and Phononic Microsystems, Sandia National Laboratories（桑迪亚国家实验室光子与声子微系统）；The Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；Quantum Information Science Section, Computational Sciences and Engineering Division, Oak Ridge National Laboratory（橡树岭国家实验室计算科学与工程部量子信息科学科）
Multi-port beamsplitters are cornerstone devices for high-dimensional quantum information tasks, which can outperform the two-dimensional ones. Nonetheless, the fabrication of such devices has been proven to be challenging with progress only recently achieved with the advent of integrated photonics. Here, we report on the production of high-quality $N \times N$ (with $N=4,7$) multi-port beamsplitters based on a new scheme for manipulating multi-core optical fibers. By exploring their compatibility with optical fiber components, we create 4-dimensional quantum systems and implement the measurem…
Exceptional points (EPs) are degeneracies of non-Hermitian operators where, in addition to the eigenvalues, corresponding eigenmodes become degenerate. Classical and quantum photonic systems with EPs have attracted tremendous attention due to their unusual properties, topological features, and an enhanced sensitivity that depends on the order of the EP, i.e. the number of degenerate eigenmodes. Yet, experimentally engineering higher-order EPs in classical or quantum domains remains an open challenge due to the stringent symmetry constraints that are required for the coalescence of multiple eig…
We present the experimental observation of an optical spring without the use of an optical cavity. The optical spring is produced by interference at a beamsplitter and, in principle, does not have the damping force associated with optical springs created in detuned cavities. The experiment consists of a Michelson-Sagnac interferometer (with no recycling cavities) with a partially reflective GaAs microresonator as the beamsplitter that produces the optical spring. Our experimental measurements at input powers of up to 360 mW show the shift of the optical spring frequency as a function of power …
Cascaded Metasurface Interferometer for Multipath Interference with Classical and Quantum Light
Paderborn University（帕德博恩大学）；Beijing Institute of Technology（北京理工大学）；Johannes Kepler University（约翰内斯·开普勒大学）；Julius-Maximilians-University of Würzburg（维尔茨堡朱利叶斯-马克西米利安大学）；Vorarlberg University of Applied Sciences（福拉尔贝格应用科学大学）；Sapienza Università di Roma（罗马大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）
We consider regimes of Spontaneous Parametric Down-Conversion both noncollinear and nondegenerate in frequencies. Parameters characterizing degrees of noncollinearity and of nondgeneracy are defined, and they are shown to be not independent of each other. At a given degree of nondegeneracy the emitted photons are shown to propagate along two different cones opening angles of which are determined by the degree of nondegeneracy. Based on this, the degree of nondegeneracy can be controlled by means of the angular selection of photons, e.g., with the help of appropriately installed slits. For such…
A single photon can be made to entangle simultaneously in its different internal degrees of freedom (DoF) -- polarization, orbital angular momentum (OAM), and frequency -- as well as in its external DoF -- path. Such entanglement in multiple DoF is known as hyperentanglement and provide additional advantage for quantum information processing. We propose a passive optical setup using $q$-plates and polarization beamsplitters to hyperentangle an incoming single photon in polarization, OAM, and path DoF. By mapping polarization DoF to a two-dimensional coin state, and path and OAM DoF to two spat…
Thin film 4H-silicon carbide (4H-SiC) is emerging as a contender for realizing large-scale optical quantum circuits due to its high CMOS technology compatibility and large optical nonlinearities. Though, challenges remain in producing wafer-scale 4H-SiC thin film on insulator (4H-SiCOI) for dense integration of photonic circuits, and in efficient coupling of deterministic quantum emitters that are essential for scalable quantum photonics. Here we demonstrate hybrid integration of self-assembled InGaAs quantum dots (QDs) based single-photon sources (SPSs) with wafer-scale 4H-SiC photonic chips …
A scheme for heralded generation of frequency-bin photonic qubits via spontaneous four-wave mixing in a system of coupled microring resonators (photonic molecule) is developed so that the qubit state is fully controlled by the frequency amplitude of the pump field. It is shown that coupling parameters of the photonic molecule can be optimized to provide generation of nearly pure heralded photons. The heralded qubit state does not depend on the microring resonator mode frequency, thereby allowing to take advantage of frequency multiplexing for improving efficiency of quantum information process…
Interference of two photons at a beamsplitter is at the core of many quantum photonic technologies, such as quantum key distribution or linear-optics quantum computing. Observing high-visibility interference is challenging because of the difficulty of realizing indistinguishable single-photon sources. Here, we perform a two-photon interference experiment using phase-randomized weak coherent states with different mean photon numbers. We place a tight upper bound on the expected coincidences for the case when the incident wavepackets contain single photons, allowing us to observe the Hong-Ou-Man…
The integration of quantum emitters with integrated photonics enables complex quantum photonic circuits that are necessary for photonic implementation of quantum simulators, computers, and networks. Thin-film lithium niobate is an ideal material substrate for quantum photonics because it can tightly confine light in small waveguides and has a strong electro-optic effect that can switch and modulate single photons at low power and high speed. However, lithium niobite lacks efficient single-photon emitters, which are essential for scalable quantum photonic circuits. We demonstrate deterministic …
The scalability of photonic implementations of fault-tolerant quantum computing based on Gottesman-Kitaev-Preskill (GKP) qubits is injured by the requirements of inline squeezing and reconfigurability of the linear optical network. In this work we propose a topologically error-corrected architecture that does away with these elements at no cost - in fact, at an advantage - to state preparation overheads. Our computer consists of three modules: a 2D array of probabilistic sources of GKP states; a depth-four circuit of static beamsplitters, phase shifters, and single-time-step delay lines; and a…
We propose a deterministic yet fully passive scheme to transfer the quantum state from a frequency-encoded photon to the spin of a quantum-dot mediated by a nanophotonic waveguide. We assess the quality of the state transfer by studying the effects of all relevant experimental imperfections on the state-transfer fidelity. We show that a transfer fidelity exceeding 95% is achievable for experimentally realistic parameters. Our work sets the stage for deterministic solid-state quantum networks tailored to frequency-encoded photonic qubits.
Photonic quantum memory, such as an atomic frequency comb (AFC), is essential to make photonic quantum computation and long distance quantum communication scalable and feasible. In standard AFC the frequency of different atoms must be stable relative to each other which presents difficulties in realizing the quantum memory. Here we propose a quantum memory using an intra-atomic frequency comb which does not require frequency stabilization. We show that the transitions between two degenerate energy levels of a single atom can be used to construct the frequency comb. The spacing between the teet…
Large-scale continuous variable (CV) cluster state is necessary in quantum information processing based on measurement-based quantum computing (MBQC). Specially, generating large-scale CV cluster state multiplexed in time domain is easier to implement and has strong scalability in experiment. Here one-dimensional (1D) large-scale dual-rail CV cluster states multiplexed both in time and frequency domains are parallelly generated, which can be further extended to three-dimensional (3D) CV cluster state by combining two time-delay NOPA systems with beamsplitters. It is shown that the number of pa…
On-demand and efficient storage of photons is an essential element in quantum information processing and long-distance quantum communication. Most of the quantum memory protocols require bulk systems in order to store photons. However, with the advent of integrated photonic chip platforms for quantum information processing, on-chip quantum memories are highly sought after. In this paper, we propose a protocol for multi-mode photonic quantum memory using only single-atom-cavity setup. We show that a single atom containing a frequency comb coupled to an optical cavity can store photons efficient…
Photonic quantum technologies such as quantum cryptography, photonic quantum metrology, photonic quantum simulators and computers will largely benefit from highly scalable and small footprint quantum photonic circuits. To perform fully on-chip quantum photonic operations, three basic building blocks are required: single-photon sources, photonic circuits and single-photon detectors. Highly integrated quantum photonic chips on silicon and related platforms have been demonstrated incorporating only one or two of these basic building blocks. Previous implementations of all three components were ma…
Large-scale quantum technologies require exquisite control over many individual quantum systems. Typically, such systems are very sensitive to environmental fluctuations, and diagnosing errors via measurements causes unavoidable perturbations. In this work we present an in situ frequency locking technique that monitors and corrects frequency variations in single photon sources based on microring resonators. By using the same classical laser fields required for photon generation as a probe to diagnose variations in the resonator frequency, our protocol applies feedback control to correct photon…
