The increasing number of qubits in quantum processors necessitates a corresponding increase in the number of control lines between the processor, which is typically operated at cryogenic temperatures, and external electronics. Scaling poses significant challenges in terms of the thermal loads, forming a major bottleneck in the realization of large-scale quantum computers. In this study, we analyze simultaneous gate operations on multiple qubits using microwaves transmitted via a single cable in a frequency-division multiplexing (FDM) scheme. By employing rectangular control microwave pulses, we reveal the contribution of drive frequency spacing to gate fidelity. Through theoretical and numerical analyses, we demonstrate that orthogonal and quasiorthogonal microwave signals suppress interference in simultaneously driven qubits, thereby ensuring high gate fidelity. Additionally, we provide design guidelines for key parameters, including pulse length, number of multiplexed microwave signals, and rotation angle, to achieve precise qubit operations. Our findings enable a scalable FDM-based microwave control scheme suitable for quantum processors with a large number of qubits.

Noise characteristics of state-of-the art light sources are crucial parameters in understanding their limitations regarding quantum applications. This work describes a method to study the electrical noise transfer of current driver sources to the intensity noise of midinfrared emission by commercial quantum and interband cascade lasers (QCLs and ICLs, respectively). A current driver with sub-shot-electrical-noise in a specific frequency range (up to 10 dB below the shot-noise level) was developed for this purpose. This enables testing of the performance of midinfrared lasers when they are driven via such a quiet pump source. By using this current driver, we identify the fundamental noise of a QCL and an ICL, which is the laser intensity noise resulting solely from the internal dynamics of the laser under test. The proposed method allows us to retrieve the noise transfer function from current to light, showing that the main limitations in observing the quantum properties of the emitted photons come from laser excess noise and poor matching between the laser and the detection system in terms of bandwidth and optical power. From the analysis of the measured parameters, we highlight current technological limitations and suggest which key features should be optimized in midinfrared systems for matching the performance required by quantum applications.

Extrinsic traps created by dopants or impurities are ubiquitous in organic semiconductors and can critically influence charge transport. Here we report a comprehensive study, using low-temperature thermally stimulated luminescence measurements complemented by quantum mechanics and molecular dynamics (QM-MD) calculations, as well as kinetic Monte Carlo (KMC) simulations, to investigate trapping and energetic relaxation of charge carriers in amorphous host-guest systems containing the widely investigated thermally activated delayed fluorescence (TADF) emitter 10-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9,9-dimethyl-9,10-dihydro-acridine (DMAC-TRZ) in two different hosts. DMAC-TRZ guest acts as a shallow trap in 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) and a deep trap in 1,3-bis (triphenylsilyl) benzene (UGH3), each forming an additional offset Gaussian density of states (DOS) distribution, as supported by the QM-MD calculations. These calculations accurately reproduce the trap depths ${\epsilon }_t$ and widths of the DOS distributions ${\sigma }_{\mathrm{DOS}}$ in the considered compositions, showing that the nominal trap depth is independent of the host-guest ratio. By experiment and KMC simulations we found that the trapping behavior differs significantly for shallow (${\epsilon }_t$ ≤ $3{\sigma }_{\mathrm{DOS}}$) and deep (${\epsilon }_t$ > $3{\sigma }_{\mathrm{DOS}}$) cases. Shallow traps do not behave as distinct traps but rather broaden the host DOS and increase the density of low-energy states, causing the average activation energy to depend on guest concentration $c_t$, in line with the “effective disorder” concept. By contrast, when a trap is deep, the energy needed to release the trapped charges to the host is independent of the guest concentration. Furthermore, for deep traps, we observe that charge detrapping occurs simultaneously via both guest-to-host and guest-to-guest charge-transfer pathways, with the latter regime becoming dominant for concentrations exceeding $c_t$ = 5%. Remarkably, this guest-guest transfer already sets in at only 1% trap concentration. We attribute this to local guest clustering and superexchange-mediated intercluster transfer.

Heavily doped graphene excels in electrical and thermal transport, far outperforming most other two-dimensional (2D) metals. Goldene, a single-atom-thick 2D metal with hexagonal lattice, has been demonstrated to possess conductivity rivaling that of heavily doped graphene. The recent synthesis of bilayer and trilayer goldene with two stacking orders provides a platform for exploring highly conductive 2D materials. Here, we investigate the electron-phonon scattering-limited electronic transport properties of these multilayer goldenes using first-principles calculations. Results show that multilayer goldenes possess significantly higher electrical and thermal conductivities than both monolayer goldene and heavily doped graphene at room temperature. A Lifshitz transition induced by hole doping or tensile strain can further enhance trilayer performance beyond the bilayer. These findings suggest that multilayer goldenes are promising candidates as conducting wires in future devices and integrated circuits, replacing bulk gold to enable miniaturization and reduce noble metal consumption.

Efficient qubit reset and leakage reduction are essential for scalable superconducting quantum computing, particularly in the context of quantum error correction. However, such operations often require additional on-chip components. Here, we propose and experimentally demonstrate a hardware-efficient approach to qubit reset and readout using a multimode Purcell filter in a superconducting quantum circuit. We exploit the inherent multimode structure of a coplanar waveguide resonator, using its fundamental and second-order modes for qubit reset and readout, respectively, thereby avoiding additional components. Implemented in a flip-chip architecture, our device achieves unconditional reset with residual excitation below 1% in 220 ns, and a leakage-reduction unit that selectively resets the second excited state within 62 ns, with a residual $|f⟩$ population of 6.1%, after accounting for the readout error. Despite the qubits being directly coupled to the filter in our configuration, the measured relaxation times are not degraded, owing to intrinsic Purcell protection provided by an auxiliary mode. To our knowledge, this work constitutes the first experimental demonstration exploiting different-order modes of a microwave resonator for distinct qubit operations, representing a new direction toward scalable, hardware-efficient quantum processor design.

Unlike other quantum hardware, photonic quantum architectures can produce millions of qubits from a single device. However, controlling photonic qubits remains challenging, even at small scales, due to their weak interactions, making nondeterministic gates in linear optics unavoidable. Nevertheless, a single photon can readily spread over multiple modes and create entanglement within the multiple modes deterministically. Rudolph’s concept of third quantization leverages this feature by evolving multiple single photons into multiple modes, distributing them uniformly and randomly to different parties, and creating multipartite entanglement without interactions between photons or nondeterministic gates. This method requires only classical communication and deterministic entanglement within multimode single-photon states and enables universal quantum computing. The multipartite entanglement generated within the third-quantization framework is nearly deterministic, where “deterministic” is achieved in the asymptotic limit of a large system size. In this work, we propose a near-term experiment using antimony donor in a silicon chip to realize third quantization. Utilizing the eight energy levels of antimony, one can generate two eight-mode single-photon states independently and distribute them to parties. This enables a random multipartite Bell-state experiment, achieving a Bell state with an upper-bound efficiency of 87.5% among 56 random pairs without nondeterministic entangling gates. This approach opens alternative pathways for silicon-based photonic quantum computing.

Atmospheric turbulence in free space affects communication links, leading to a deterioration of the frequency stability of frequency-transmission systems. We establish a relation between the effect of phase fluctuations induced by atmospheric turbulence and the instability of frequency transmission in free space. Considering the optical coupling efficiency as an intermediary between the frequency-transmission system and atmospheric turbulence, we analyze the transfer behavior of frequency stability under varying turbulence conditions, combined with the Gamma-Gamma channel statistical model. In this study, we experimentally validate the model over a 1 km free-space link. Frequency stabilities of $4.1\times {10}^{-12}$ at 1 s and $4.7\times {10}^{-15}$ at 1000 s are demonstrated. The observed optical power fluctuations and the system Allan deviation (ADEV) are in excellent agreement with the simulation results, fully confirming the model’s accuracy and applicability in assessing the degradation effects of atmospheric turbulence. This work provides a theoretical tool for quantitatively analyzing the limits of frequency transmission in complex atmospheric environments and offers important guidance for optimizing the design of urban free-space optical frequency transfer systems.

We present a practical design framework for high-fidelity quantum control in coupled Kerr-nonlinear oscillators, directly addressing the challenge of spectral crowding. We show that systematic spectral degeneracies, which hinder selective addressing, are a direct consequence of rational Kerr-nonlinearity ratios ($K_1/K_2$). Our solution is a universal architectural principle: engineer this ratio to be a complex rational value, approximating an incommensurate number to systematically eliminate parasitic resonances. Using a Magnus expansion, we derive a complete effective Hamiltonian, including all Stark-shift corrections, to accurately target transitions. We numerically validate this framework by demonstrating protocols for the deterministic synthesis of NOON states, and high-photon-number Fock states, achieving ideal fidelities exceeding $\mathcal{F}>99.7\mathrm{\%}$. The protocols are shown to be robust against environmental decay and thermal effects. This work provides an architectural blueprint for bosonic processors in circuit quantum electrodynamics and establishes foundational principles that could inform future designs of multimode quantum systems.

In this work, we demonstrate theoretically and numerically that propagating waves can be fully converted into surface waves, and vice versa, using an aperiodic metasurface composed of simple, electrically small metallic elements loaded with reactive components. The proposed approach achieves nearly 100% conversion efficiency and even enables operation in the superdirective regime. We show that these metasurfaces can be designed in a modular fashion, allowing for straightforward cascading and the realization of multifunctional responses without the need for global optimization. Specifically, employing this modular methodology, we design a metasurface that converts an arbitrary incident propagating wave into a surface wave, guides it along the surface, and reradiates the received power in any desired direction with a tailored wave-front shape. The proposed technique can be used in antenna engineering and in advanced designs of reconfigurable intelligent surfaces.

High-fidelity coherent population transfer plays a vital role in the realization of quantum memories. However, population transfer with high performance across a broad frequency range is still challenging due to the finite Rabi coupling strength limited by laser powers. Here we propose a population-transfer scheme by suturing adiabatic control pulses where each pulse covers a certain frequency interval and that are connected in a way that neighboring adiabatic pulses have opposite chirping directions. Taking the widely used hyperbolic-square-hyperbolic pulse as an example, we demonstrate that rapid and robust population transfer can be achieved. The transfer bandwidth scales linearly with the number of suture pulses while maintaining high fidelity, even at the suture points where adiabaticity breaks down. Crucially, these pulses can be realized by a single laser by means of temporal multiplexing. For a given bandwidth, this strategy substantially reduces the operational time, which is necessary for on-demand read out and suppression of decoherence effects. Our scheme enables a dramatic increase in multimode storage capacity, and paves the way for realizing practical quantum networks.

Electrical control of magnetic order by current-induced spin-orbit torque (SOT) plays a pivotal role in spintronics. Recently, SOT in heavy metal/magnetic insulator bilayers have gained increasing interest due to their low magnetic damping and ultrafast spin dynamics, making them ideal for applications in magnon-based spintronics. Here, we realized SOT-induced perpendicular magnetization switching in insulating compensated ferrimagnetic ${\mathrm{Gd}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/\mathrm{Pt}$ heterostructures with high compensation temperature. The SOT-induced switching shows opposite switching polarity as temperature across the magnetic compensation point. Moreover, by harmonic Hall voltage measurements, we quantitatively determine the temperature dependence of the dampinglike SOT effective field and find a pronounced enhancement near compensation that scales with $1/M_s$. Of note, we further achieve ultrafast current-induced magnetization switching using electrical pulses as short as 10 ns, demonstrating high-speed SOT control in a ferrimagnetic insulator. These results establish insulating ferrimagnets as a promising platform for high-speed magnon-based spintronic devices operating at and above room temperature.

Surface acoustic waves (SAWs), as elastic waves generated by piezoelectric or piezomagnetic media, have been used in gyroscopes for more than 40 years due to their unique propagation characteristics. However, their working principle, based on Coriolis effects, has become increasingly ineffective for addressing modern sensing challenges in complex scenarios. Fortunately, recent advancements in quantized SAWs offer a promising solution: SAWs operating at extremely low pump powers (approximately at the single-phonon level) can exhibit substantial quantum coherence, enabling investigations into the fundamental limits of SAW gyroscopes as constrained by the Heisenberg uncertainty relation. In particular, when multiple SAWs couple to a common waveguide at distinct locations, the nonlocality arising from the spatial separation among coupling points induces directional coupling between the SAWs. To elucidate this directionality, we propose a quantum gyroscope characterized by multiple-point couplings. Unlike traditional single-point coupling designs, our gyroscope exhibits distinctive time-delayed dynamics that depend on the system’s topologies. Through a comprehensive analysis of all possible topologies, we observe that the directional coupling implies an inherent nonreciprocal transfer. This nonreciprocity confers significant advantages on our gyroscope compared with traditional designs, notably increasing both the signal-to-noise ratio and sensitivity. Specifically, it enables the extraction of output signals that would otherwise be obscured by noise. Consequently, our findings suggest that systems with multiple-point couplings and the associated nonreciprocity can serve as valuable resources for advancing quantum sensing technologies.

The active stabilization of polarization channels is a task of growing importance as quantum networks move to deployed demonstrations over existing fiber infrastructure. However, the uniquely strict requirements for high-fidelity qubit transmission complicate the extent to which classical solutions may apply to future quantum networks, particularly in terms of recognizing noise sources present in low-flux, nonunitary channels. Here we introduce an in situ benchmarking approach that augments a classical polarization tracking system, limited to unitary correction, with simultaneously transmitted quantum light for ancilla-assisted process tomography of the full quantum map. Implemented in a quantum local-area network, our method uses the reconstructed map both to validate the classical compensation and to expose noise sources it fails to capture. A sliding measurement window that continuously updates the estimated quantum process further increases sensitivity to rapid channel fluctuations. Our results should unlock new opportunities for in situ channel characterization in quantum-classical coexistence networks.

Circularly polarized light (CPL) has diverse applications in a myriad of fields. Crucial to CPL technologies is the ability to discern between left- and right-handed CPL through CPL-sensitive photodetectors. Here, we studied chiral photodetectors based on two enantiomers of chiral bulk heterojunctions (BHJ) consisting of fullerenes (${\mathrm{PC}}_{71}\mathrm{BM}$), chiral helicene molecules ($\mathrm{aza}[6]\mathrm{H}$), and π-conjugated donor-acceptor copolymers (F8BT), which exhibit significant circular dichroism (CD). We found that the photocurrent (PC) in the chiral photodiode is sensitive to the impinging light helicity and the chiral BHJ handedness, showing a large dissymmetry $g_{\mathrm{PC}}$-factor of ∼20%. Using optical and optoelectronic methods, we demonstrate that the device PC dissymmetry spectrum does not follow the CD spectrum of the chiral BHJ, which contrasts with other CPL photodetectors that rely on large CD, and is sensitive to an applied magnetic field. The methods include chiroptical response, steady-state PC spectroscopy, and time-of-flight transient PC. We show that the PC dissymmetry is caused by the chirality-induced spin selectivity (CISS) in the active layer, where it serves as a spin filter in the photogeneration and subsequent recombination processes across the polymer/fullerene interface, rather than the circularly polarized light absorption in the device or the spin-aligned carrier mobility. The CISS process is best manifested in the measured dissymmetry of the photocarrier’s lifetime under circularly polarized light that is influenced by a magnetic field. Our experiments could be used to prove the existence of CISS in other chiral materials, where the chiral chromophores are randomly oriented.

We have developed a compact magneto-optical trap (MOT) that employs a two-dimensional (2D) quadrupole magnetic field generated by a double-layer planar coil with a single current source. The combination of the 2D quadrupole magnetic field with the mirror MOT expands the capture region, thereby enabling the trapping of a vast number of atoms and achieving a high optical depth (OD). Our results demonstrate that an elongated cold atomic cloud can contain up to $2.8\times {10}^8$ cold ${}^{87}\mathrm{Rb}$ atoms, attaining an OD of up to 33. This simplified and compact MOT presents an alternative technical solution for various applications involving quantum optics with cold atoms, preparation of degenerate quantum gases, as well as advancements in quantum sensing and metrology, among others.