Manipulation Of Quantum States Research Articles

Instrumental distortions in quantum optimal control.

Quantum optimal control methods, such as gradient ascent pulse engineering (GRAPE), are used for precise manipulation of quantum states. Many of those methods were pioneered in magnetic resonance spectroscopy, where instrumental distortions are often negligible. However, that is not the case elsewhere: the usual jumble of cables, resonators, modulators, splitters, amplifiers, and filters can and would distort control signals. Those distortions may be non-linear; their inverse functions may be ill-defined and unstable; they may even vary from one day to the next and across the sample. Here we introduce the response-aware gradient ascent pulse engineering framework, which accounts for any cascade of differentiable distortions within the GRAPE optimization loop, does not require filter function inversion, and produces control sequences that are resilient to user-specified distortion cascades with user-specified parameter ensembles. The framework is implemented into the optimal control module supplied with versions 2.10 and later of the open-source Spinach library; the user needs to provide function handles returning the actions by the distortions and, optionally, parameter ensembles for those actions.

One-Dimensional Electron Gas Confined along Nanowrinkles in a Unidirectional Charge Density Wave Material.

Two-dimensional (2D) materials inherently exhibit instabilities. Structurally, this may lead to modulations along the third dimension, e.g., wrinkles. Electronically, 2D instabilities can manifest themselves as charge density waves (CDWs). Although wrinkles can alter anisotropic electronic structures susceptible to forming CDWs, less is known about their impact on broken-symmetry ground states. Here, using scanning tunneling microscopy and spectroscopy, we investigate the CDW states on the wrinkled surface of DyTe3. We identify elongated, parallel nanoscale wrinkles stabilized by ribbon-shaped defects. Interestingly, the CDW order persists across the nanowrinkles with a gradual phase shift but is locally suppressed near the defects, where phase windings occur. In addition, these defects induce quantum confinement effects along the nanowrinkles, indicating the presence of one-dimensional metallic states with hole-like dispersion, while angle-resolved photoemission spectroscopy identifies a gap along the wrinkle direction. We ascribe this discrepancy to strain-induced changes in the Fermi surface, which lead to the closure of the gap at the sites of the nanowrinkles. Taken together, our results underscore the complex interplay between structural features and Fermi surface topology, allowing for the deliberate manipulation of quantum states in strongly correlated systems via local crystal deformations.

Quantum metamaterials: Applications in quantum information science

Metamaterials are a class of artificially engineered materials with periodic structures possessing exceptional properties not found in conventional materials. This definition can be extended when we introduce a degree of freedom by adding quantum elements such as quantum dots, cold atoms, Josephson junctions, and molecules, making metamaterials highly valuable for various quantum applications. Metamaterials have been used to achieve invisibility cloaking, super-resolution, energy harvesting, and sensing, among other applications. Most of these applications are performed in the classical regime. Metamaterials have gradually made their way into the quantum regime since the advent of quantum computing and quantum sensing and imaging. Quantum metamaterials are a relatively new technology, and their use in quantum information processing has proliferated. We restrict this study to quantum state manipulation and control, quantum entanglement, single photon generation, quantum state switching, quantum state engineering, quantum key distribution, quantum algorithms, orbital angular momentum, and quantum imaging. Considering these developments, we examine the theory, fabrication, and applications contributing to quantum information processing and how quantum metamaterials contribute to this field. We find that the ability to harness the unique properties of metamaterials to drive these applications is of great importance, as they have the potential to unlock new possibilities for revolutionizing quantum information processing, bringing the world closer to practical quantum technologies with unprecedented capabilities. We conclude by suggesting possible future research directions.

Power of quantum measurement in simulating unphysical operations

The manipulation of quantum states through linear maps beyond quantum operations has many important applications in various areas of quantum information processing. Current methods simulate unphysical maps by sampling physical operations according to classically determined probability distributions. In this work, we show that using quantum measurement instead leads to lower simulation costs for general Hermitian-preserving maps. Remarkably, we establish the equality between the simulation cost and the well-known diamond norm, thus closing a previously known gap and assigning diamond norm a universal operational meaning for all Hermitian-preserving maps. We demonstrate our method in two applications closely related to error mitigation and quantum machine learning, where it exhibits a favorable scaling. These findings highlight the power of quantum measurement in simulating unphysical operations, in which quantum interference is believed to play a vital role. Our work paves the way for more efficient sampling techniques and has the potential to be extended to more quantum information processing scenarios. Published by the American Physical Society 2025

Nonresonant Electric Quantum Control of Individual On-Surface Spins.

Quantum control techniques play an important role in manipulating and harnessing the properties of different quantum systems, including isolated atoms. Here, we propose to achieve quantum control over a single on-surface atomic spin using Landau-Zener-Stückelberg-Majorana (LZSM) interferometry implemented with scanning tunneling microscopy (STM). Specifically, we model how the application of time-dependent, nonresonant ac electric fields across the STM tip-surface gap makes it possible to achieve precise quantum state manipulation in an isolated Fe^{2+} ion on a MgO/Ag(100) surface. We propose a protocol to combine Landau-Zener tunneling with LZSM interferometry that permits one to measure the quantum spin tunneling of an individual Fe^{2+} ion. The proposed experiments can be implemented with ESR-STM instrumentation, opening a new venue in the research of on-surface single spin control.

Atomic quadrupolar fluorescence in the presence of a spherical nanoantenna: cesium 6S1/2 − 6D5/2

We examine the fluorescence of a quadrupolar transition occurring in a three-level atom near a spherical nanoantenna with plane-wave excitation; the atom can be only excited by means of a quadrupolar transition, and it can decay either by a direct quadrupolar transition or a ladder decay composed of two dipolar transitions. Since dipolar transitions are unavoidable, fluorescence from them is also studied. Specifically, we analyze the fluorescence rates of the radiative transitions of the cesium atom (6S1/2−6D5/2), as well as the involving competing processes, namely, the excitation rate and quantum yield. In relation to the case without a nanoantenna: (1) the quadrupolar quantum yield can be enhanced by about 2.55 orders of magnitude; (2) the excitation rate of the quadrupolar transition reaches an enhancement between 2 and 3.7 orders of magnitude; (3) because of the simultaneous enhancement of the excitation rate and quantum yield, the quadrupolar fluorescence rate can be enhanced by 4.7 orders of magnitude, enabling the practical detection of the fluorescence from the quadrupolar transition, whereas the dipolar fluorescence rates are augmented about 2.18 orders of magnitude. These findings occur when the atom is placed in an interval less than 10 nm from the surface of the nanoantenna. In addition, even in the presence of the nanoantenna, the quadrupolar fluorescence rate is smaller than the dipolar one; the ratio of these quantities with respect to its free-space value can be improved at most 2.3 orders of magnitude. Our setup is simple for practical implementation; hence, our work might impact applications related to atomic spectroscopy and sensing as well as control and manipulation of light emission and quantum states.

Measurement of the time-domain Landau-Zener-Stückelberg-Majorana interference sidebands in an <sup>87</sup>Sr optical lattice clock

<sec>Landau-Zener-Stückelberg-Majorana (LZSM) interference has significant application value in quantum state manipulation, extending quantum state lifetime, and suppressing decoherence. Optical lattice clock, with a long coherence time, increases the likelihood of experimentally observing time-domain LZSM interference. Although time-dominant Landau-Zener (LZ) Rabi oscillations have already been observed in optical lattice clock, the time-dominant LZSM interference sidebands in optical lattice clock remain unexplored. This study is based on an <sup>87</sup>Sr optical lattice clock. By periodically modulating the frequency of the 698-nm clock laser and optimizing the parameters of the optical clock system, LZ transitions are achieved under the fast-passage limit (FPL). During the clock detection, two acoustic optical modulators (AOMs) are employed: AOM1 that compensates for the frequency drift of the clock laser and operates continuously throughout the experiment, and AOM2 that performs traditional clock transition detection and generates a cosine modulation signal by using an external trigger from the RF signal generator in Burst mode. Ultimately, the periodically modulated 698-nm clock laser with a frequency of <inline-formula><tex-math id="M1">\begin{document}$\omega (t) = \cos \left[ {\displaystyle\int {\left( {{\omega _{\text{p}}} - A{\omega _{\text{s}}}\cos {\omega _{\text{s}}}t} \right)dt} } \right]$\end{document}</tex-math></inline-formula> is used to probe atoms, and the Hamiltonian is <inline-formula><tex-math id="M2">\begin{document}$ {\hat H_n}(t) = \dfrac{h}{2}[\delta + A{\omega _{\text{s}}}\cos ({\omega _{\text{s}}}t)]{\hat \sigma _z} + \dfrac{{h{g_n}}}{2}{\hat \sigma _x} $\end{document}</tex-math></inline-formula>.</sec><sec>As the modulated laser interacts with the atoms, the interference phenomenon is exhibited in the time domain; adjusting the clock laser detuning allows for probing the time-domain LZSM interference sideband spectra at different detection times. The results show that the time-domain LZSM interference sideband consists of multiple sidebands. Specifically, ±<i>kth</i> order sidebands can be observed at <i>δ</i>/<i>ω</i><sub>s</sub> = <i>k</i>, where <i>k</i> is an integer, representing constructive interference. Additionally, due to the different LZ Rabi oscillation periods for each sideband, the excitation fractions of different sidebands are also different, resulting in different excitation fractions for sidebands at the same clock detection time. When scanning the frequency of the clock laser, small interference peaks will appear next to the +1st, +4th, +5th, +6th<i>,</i> –3th and –4th order sidebands when detection time is an integer period. These peaks all appear on the right side of the sidebands, thus breaking the symmetry of LZSM interference sidebands. In contrast, when the detection time is a half-integer period, the interference sidebands exhibit symmetric distribution. This phenomenon mainly arises from the effective dynamical phase accumulated during the LZSM interference evolution. Moreover, the excitation fraction is higher than that at half-integer period, which holds potential application value in state preparation research. The experimental results are in excellent agreement with theoretical simulations, confirming the feasibility of conducting time-domain LZSM interference studies on the optical lattice clock. In the future, by further suppressing clock laser noise, the optical lattice clock will provide an ideal experimental platform for studying the effects of noise on LZ transition.</sec>

High-order coherence of super-bunching squeezed thermal states and squeezed number states of light fields

The bunching and antibunching effects of optical fields reflect the spatiotemporal correlations of photons, serving as key indicators to distinguish quantum statistics between classicality and non-classicality, and playing an essential role in quantum information processing and precision measurement. In this paper, we investigate the super-bunching and antibunching effects of the full-time-delay higher-order coherence function <i>g</i><sup>(<i>n</i>)</sup> for squeezed thermal states and squeezed number states based on a multi-cascaded Hanbury Brown–Twiss single-photon detection scheme.<br>Under ideal conditions, the high-order coherence of squeezed thermal states and squeezed number states is analyzed with varying compression parameter <i>r</i>, average photon number<i>α</i>, and squeezed photon number <i>n</i>. The results indicate that when the compression parameter $r \in[0,1]$, the squeezed thermal state exhibits a significant super-bunching effect, with super-bunching values of each order given by <i>g</i><sup>(2)</sup>= 9.98×10<sup>5</sup>,<i>g</i><sup>(3)</sup>= 8.98×10<sup>6</sup>,<i>g</i><sup>(4)</sup>= 8.96×10<sup>12</sup>,<i>g</i><sup>(5)</sup>= 2.24×10<sup>14</sup>.The squeezed number state exhibits a continuous transition from antibunching to bunching behavior, with coherence degrees at various orders given as <i>g</i><sup>(2)</sup>∈[1.60×10<sup>-5</sup>, 1.09], <i>g</i><sup>(3)</sup>∈[9.02×10<sup>-6</sup>, 1.16], <i>g</i><sup>(4)</sup>∈[4.75×10<sup>-6</sup>, 1.22], <i>g</i><sup>(5)</sup>∈[9.39×10<sup>-6</sup>, 1.30]）．<br>Simultaneously, the study analyzed the high-order photon coherence of squeezed thermal states and squeezed number states under experimental conditions, taking into account background noise <i>γ</i> and detection efficiency η．When detection efficiency is relatively low and background noise is substantial, the higher-order coherence of squeezed thermal states with smaller average photon number <i>α</i> is disturbed by background noise, yet still maintains good super-bunching characteristics; however, when the average photon number <i>α</i> becomes large, limited by the dead time of single-photon detectors, it is challenging to accurately obtain all the information of the squeezed number state light field, resulting in measurement results that deviate from the ideal values. When the average photon number is <i>α</i>=0.5, the super-bunching effects reach their maximum values of <i>g</i><sup>(2)</sup>= 2.149、<i>g</i><sup>(3)</sup>= 6.389和<i>g</i><sup>(4)</sup>= 23.228, corresponding respectively to the squeezing degrees <i>S</i><sup>(2)</sup>= 5.47、<i>S</i><sup>(2)</sup>= 4.86和<i>S</i><sup>(2)</sup>= 4.43. Furthermore, by adjusting the number of squeezed photons <i>η</i> and the squeezing degree S of the squeezed number state light field, a continuous and wide-ranging variation of the high-order coherence function can be achieved, transitioning from anti-bunching to super-bunching effects. Additionally, under conditions of high environmental noise and low detection efficiency, higher-order coherence exhibits greater sensitivity to variations in optical field parameters compared to lower-order coherence. Furthermore, squeezed number states with multi-photon characteristics are less susceptible to disturbances from background noise, demonstrating stronger robustness.<br>In addition, the variation characteristics of the high-order photon coherence function of the squeezed thermal state light field under full time-delay conditions were investigated. The full time-delay high-order coherence <i>g</i><sup>(<i>n</i>)</sup> of the squeezed thermal state light field near the coherence time range $\tau_{\mathrm{STS}}$ is significantly higher than that of the classical thermal state light field. Even when a significant time delay is introduced in one of the optical paths, partial synchronization among photons can still maintain a certain correlation strength. Although unsynchronized photons lead to an overall reduction in coherence, the coherence remains higher than the theoretical predictions for thermal states under identical conditions.<br>Building on the theoretical framework established in this work, future experiments may focus on adjusting the pump power, intracavity loss, and crystal temperature of optical parametric amplifiers to jointly control the squeezing degree and mean photon number, enabling stable generation of squeezed thermal states across different parameter regimes. Additionally, precise measurement of higher-order coherence could be achieved using cascaded HBT detection systems with multiple inputs and high temporal resolution.<br>In summary, by considering environmental noise, detection efficiency, and time delay, and through the regulation of the average photon number, the number of squeezed photons, and the squeezing parameter. This approach enables the preparation of super-bunching squeezed thermal states and squeezed number states whose higher-order coherence can be continuously tuned over a wide range, facilitating efficient quantum state preparation and manipulation, as well as high-resolution quantum imaging.

Applications of B-spline method in precise structure calculation of few-electron atoms

The precise spectroscopy of few-electron atoms plays a pivotal role in advancing fundamental physics, encompassing the verification of quantum electrodynamics (QED) theory, the determination of finestructure constants, and the exploration of nuclear properties. With the rapid development of precision measurement techniques, the demand for atomic structure data has evolved from mere confirmation of existence to the pursuit of unprecedented accuracy. To meet the growing needs for precision spectroscopy experiments, we have developed a series of high-precision theoretical methods based on B-spline basis sets, including the non-relativistic configuration interaction (B-NRCI) method, the correlated B-spline basis functions (C-BSBFs) method, and the relativistic configuration interaction (B-RCI) method. These methods leverage the unique properties of B-spline functions, such as locality, completeness, and numerical stability, to accurately solve the Schrödinger and Dirac equations for few-electron atoms.<br>Our methods have yielded significant results, particularly for helium and helium-like ions. Using these methods, we have obtained accurate energies, polarizabilities, tune-out wavelengths, and magic wavelengths. Specifically, we have achieved high-precision determinations of the energy spectra of helium, providing vital theoretical support for related experimental research. Additionally, we have made highprecision theoretical predictions of tune-out wavelengths, paving the way for new tests of QED theory. Furthermore, we have proposed effective theoretical schemes to suppress Stark shifts, thereby facilitating high-precision spectroscopy experiments of helium.<br>The B-spline-basis methods reviewed in this paper have proven exceptionally effective in highprecision calculations for few-electron atoms. These methods have not only provided crucial theoretical support for precision spectroscopy experiments but have also paved new avenues for testing QED. Their ability to handle large-scale configuration interactions and incorporate relativistic and QED corrections makes them versatile tools for advancing atomic physics research. In the future, the high-precision theoretical methods grounded in B-spline basis sets are poised to expand into frontier areas, including quantum state manipulation, nuclear structure property determination, ultracold molecule formation, and new physics exploration, thereby continuously driving the progress of precision measurement physics.

Particle-Assisted Deep Reinforcement Learning for Quantum State Manipulation

Particle-Assisted Deep Reinforcement Learning for Quantum State Manipulation

A Three-User Fully Connected Quantum Network Based on Hyperentanglement

Hyperentanglement, as a high-dimensional quantum entanglement phenomenon across multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relations simultaneously across multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. Based on this, this paper establishes a hyperentangled fully connected quantum network, realizing polarization and time-bin degree-of-freedom hyperentanglement through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100 km of entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, we verified that this network supports quantum key distribution over distances exceeding 50 km between users. These results confirm the feasibility of a hyperentangled fully connected quantum network and demonstrate the potential for constructing large-scale metropolitan networks using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. While quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a significant challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguide, the three-user hyperentangled quantum network constructed in this work provides a new solution for the development of large-scale metropolitan networks for high-dimensional quantum information networks, and it is expected to offer a new platform for quantum tasks such as superdense coding and quantum teleportation

Robust multistate quantum control with minimal additional coupling

Abstract The multistate stimulated Raman adiabatic passage (STIRAP) is an efficient technique to achieve a selective and accurate population transfer in a chainwise-linked system. However, their efficiency is imperfect due to the nonadiabatic losses from the long runtime of the adiabatic evolution. Here, we focus on realizing a perfect and robust coherent control of the quantum states with optimal shortcut to adiabaticity in a realistic five-state hybrid quantum system. In particular, the optimal shortcut field requires minimal additional coupling (only one coupling strength) to accelerate the adiabatic evolution in this five-state system. Compared to the original STIRAP, the optimal shortcut shows the ultra-high fidelity of quantum state manipulations even though the control parameters of the Hamiltonians are changed in different ways. Furthermore, we study the efficiency of the optimal shortcut field technique in the presence of various experimental errors, such as systematic error, Rabi frequency error, and coupling strength error, and it features a broad range of high efficiencies above 99.9%, showing its robustness against the above errors. The results might shed insight on the further applications of shortcuts to adiabaticity on robust quantum information processing in multi-level quantum systems.

Integrating Self-Initialized Local Thermalizing Lindblad Operators for Variational Quantum Algorithm with Quantum Jump: Implementation and Performance.

Quantum computing holds great potential for simulating quantum systems, such as molecular systems, due to its inherent ability to represent and manipulate quantum states. However, simulating nonunitary dynamics of open quantum systems on a quantum computer is still challenging. Here, we present a scheme denoted as VQS-QJ-LTLME, which adopts the trajectory average of quantum jump Monte Carlo wave function variational evolution to evolve the system's density matrix and local thermalizing Lindblad operators to describe the system-environment interactions. This combination allows the quantum circuit to be initialized after a period of evolution, thereby eliminating the accumulation of errors. The VQS-QJ-LTLME algorithm requires only log2(n) qubits for system size n and holds a time complexity of , making it particularly suitable for operation on noisy intermediate-scale quantum devices. To accelerate the Monte Carlo sampling process in VQS-QJ-LTLME, we introduce an efficient sampling method, named No-evolution sampling (NES). The VQS-QJ-LTLME aided by NES requires simulating only n3 + 1 trajectories on quantum computers, and then makes 106 to 107 samplings on classical computers in a few seconds. To demonstrate the performance of the VQS-QJ-LTLME algorithm, we simulate the dynamics of a two-level spin-boson model and a four-level reduced Fenna-Matthews-Olson system with real superconducting quantum computers and classical simulators. It is shown that the simulations produced by VQS-QJ-LTLME algorithm align closely with those obtained from the purely classical methods.

Kerr nonlinearity-induced nonreciprocal Einstein–Podolsky–Rosen steering in a cavity magnonic system

Abstract We propose to utilize magnon Kerr nonlinearity to generate and control microwave–microwave Einstein–Podolsky–Rosen (EPR) steering in a cavity magnonic system consisting of two microwave cavities and an yttrium iron garnet (YIG) sphere, where the magnon mode in the YIG sphere is driven by an electromagnetic field. The results show that Kerr nonlinearity of the magnon could not only sensibly induce enhanced entanglement of two microwave fields but also produce asymmetric EPR steering with different ratios of two damping rates and coupling constants. Moreover, it is found that the nonreciprocity of the steady-state EPR steering is obtainable by controlling the sign of the magnon Kerr parameter, which could be tuned from positive to negative by changing the direction of the static magnetic field. The demonstrated nonreciprocal EPR steering is of fundamental interest for the manipulation of quantum states, and may provide potential applications in quantum information tasks.

Ramsey interferometry of nuclear spins in diamond using stimulated Raman adiabatic passage

Abstract We report the first experimental demonstration of stimulated Raman adiabatic passage (STIRAP) in nuclear-spin transitions of 14N within nitrogen-vacancy color centers in diamond. It is shown that the STIRAP technique suppresses the occupation of the intermediate state, which is a crucial factor for improvements in quantum sensing technology. Building on that advantage, we develop and implement a generalized version of the Ramsey interferometric scheme, employing half-STIRAP pulses to perform the necessary quantum-state manipulation with high fidelity. The enhanced robustness of the STIRAP-based Ramsey scheme to variations in the pulse parameters is experimentally demonstrated, showing good agreement with theoretical predictions. Our results pave the way for improving the long-term stability of diamond-based sensors, such as gyroscopes and frequency standards.

Efficient implementation of quantum permutation algorithm using a polar SrO molecule in pendular states

Quantum algorithms offer more enhanced computational efficiency in comparison to their classical counterparts when solving specific tasks. In this study, we implement the quantum permutation algorithm utilizing a polar molecule within an external electric field. The selection of the molecular qutrit involves the utilization of field-dressed states generated through the pendular modes of SrO. Through the application of multi-target optimal control theory, we strategically design microwave pulses to execute logical operations, including Fourier transform, oracle U f operation, and inverse Fourier transform within a three-level molecular qutrit structure. The observed high fidelity of our outcomes is intricately linked to the concept of the quantum speed limit, which quantifies the maximum speed of quantum state manipulation. Subsequently, we design the optimized pulse sequence to successfully simulate the quantum permutation algorithm on a single SrO molecule, achieving remarkable fidelity. Consequently, a quantum circuit comprising a single qutrit suffices to determine permutation parity with just a single function evaluation. Therefore, our results indicate that the optimal control theory can be well applied to the quantum computation of polar molecular systems.

Hybrid III-V/Silicon Quantum Photonic Device Generating Broadband Entangled Photon Pairs

The demand for integrated photonic chips combining the generation and manipulation of quantum states of light is steadily increasing, driven by the need for compact and scalable platforms for quantum information technologies. While photonic circuits with diverse functionalities are being developed in different single material platforms, it has become crucial to realize hybrid photonic circuits that harness the advantages of multiple materials while mitigating their respective weaknesses, resulting in enhanced capabilities. Here, we demonstrate a hybrid III-V/silicon quantum photonic device combining the strong second-order nonlinearity and direct band gap of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the spontaneous parametric down-conversion (SPDC) of photon pairs into an AlGaAs source and their vertical routing to an adhesively bonded silicon-on-insulator circuitry, within an evanescent coupling scheme managing both polarization states. This enables the on-chip generation of broadband (>40 nm) telecom photons by type-0 and type-2 SPDC from the hybrid device, at room temperature and with internal pair generation rates exceeding 105s−1 for both types, while the pump beam is strongly rejected. Two-photon interference with 92% visibility (and up to 99% upon 5-nm spectral filtering) proves the high energy-time entanglement quality of the produced quantum state, thereby enabling a wide range of quantum information applications on chip, within a hybrid architecture compliant with electrical pumping and merging the assets of two mature and highly complementary platforms in view of out-of-the-lab deployment of quantum technologies. Published by the American Physical Society 2024

Realization of multi-transverse-mode squeezed optical frequency combs with Gouy phase compensation

Multimode quantum light fields significantly enhance quantum state manipulation and communication capabilities by expanding the dimensionality of the Hilbert space. In this work, we elaborately design a non-horizontal cavity suitable for a Gouy phase-compensated synchronously pumped optical parametric oscillator. By injecting an optical frequency comb in HG10 mode into the cavity as the seed, we demonstrate the simultaneous generation of a bright squeezed optical frequency comb in HG10 mode and a vacuum squeezed optical frequency comb in HG01 mode. The coexistence of amplitude quadrature squeezed fields in these two orthogonal first-order Hermite-Gaussian transverse modes also suggest the presence of quadrature entanglement between the two first-order Laguerre-Gaussian modes, LG0 + 1 and LG0 - 1. This research underscores the capability of one-step generation of multi-transverse-mode squeezed optical frequency combs using a single cavity, marking a significant stride in the realm of quantum optics.

The Floquet Fluxonium Molecule: Driving Down Dephasing in Coupled Superconducting Qubits

High-coherence qubits, which can store and manipulate quantum states for long times with low error rates, are necessary building blocks for quantum computers. Here we propose a driven superconducting erasure qubit, the Floquet fluxonium molecule, which minimizes bit-flip rates through disjoint support of its qubit states and suppresses phase flips by a novel second-order insensitivity to flux-noise dephasing. We estimate the bit-flip, phase-flip, and erasure rates through numerical simulations, with predicted coherence times of approximately 50 ms in the computational subspace and erasure lifetimes of about 500μs. We also present a protocol for performing high-fidelity single-qubit rotation gates via additional flux modulation, on timescales of roughly 500 ns, and propose a scheme for erasure detection and logical readout. Our results demonstrate the utility of drives for building new qubits that can outperform their static counterparts. Published by the American Physical Society 2024

Manipulation of High-Fidelity Sidebands under Large Detuning by Floquet Technology: Application to Multi-Mode Cooling

Abstract The Floquet technology, a powerful way to manipulate quantum states, is employed to drive sidebands transition under large detuning. Our results demonstrate that high fidelities over 99% can be achieved through optimizing suitable modulation frequencies under large detuning. We observe high-fidelity transitions within a high bandwidth by utilizing a single modulation frequency and reveal that this capability is due to the emergence of a flat-band structure in the bandwidth range. The key finding of high-fidelity sideband manipulation under large detuning is experimentally confirmed in nuclear magnetic resonance platform. Finally, we propose a new parallel sideband cooling scheme that enables simultaneous cooling of multiple motional modes. This approach improves the cooling rate compared to conventional schemes with fixed laser frequency and power, and eliminates the need for mode-specific addressing. Our Floquet parallel scheme is applicable to any harmonic oscillator system and is not limited by bandwidth in theory.