Lightsails are a promising spacecraft concept that can reach relativistic speeds via propulsion by laser light, allowing travel to nearby stars within a human lifetime. The success of a lightsail mission requires that any motion in the plane transverse to the propagation direction is bounded and damped for the entire acceleration phase. Here we demonstrate that a previously unappreciated relativistic force, which generalizes the Poynting-Robertson effect, can passively damp this transverse motion. We show that this purely optical effect can be enhanced by 2 orders of magnitude compared to the effect on plane-mirror sails by judicious design of the scattering response. We thus demonstrate that exploiting relativistic effects may be a practical means to control the motion of lightsails.

We perform two-tone spectroscopy on quantum circuits, where high-frequency radiation is generated by a voltage-biased superconductor-normal-superconductor Josephson junction and detection is carried out by an ancillary microwave resonator. We implement this protocol on two different systems, a transmon qubit and a $\lambda /4$ resonator. We demonstrate that this two-tone Josephson spectroscopy operates well into the millimeter-wave band, reaching frequencies larger than 80 GHz, and is well suited for probing highly coherent quantum systems.

Charge sensing is a sensitive technique for probing quantum devices, of particular importance for spin-qubit readout. To achieve good readout sensitivities, the proximity of the charge sensor to the device to be measured is a necessity. However, this proximity also means that the operation of the device affects, in turn, the sensor tuning and ultimately the readout sensitivity. We present an approach for compensating for this crosstalk effect allowing for the gate voltages of the measured device to be swept in a 1-V $\times$ 1-V window while maintaining a sensor configuration chosen by a Bayesian optimizer. Our algorithm will hopefully be a major contribution to the suite of fully automated solutions required for the operation of large quantum device architectures.

Acoustic metasurfaces have attracted significant interest due to their unique capabilities for wave-field manipulation, opening up novel avenues for a wide range of applications. Unlike conventional metasurfaces employing local phase-shifting units, an emerging approach based on power-flow-conformal design has emerged for sound redirection with higher efficiency. In this work, we present underwater metasurfaces designed via the power-flow-tracing methodology that enable precise tailoring of complex reflection fields. As a proof of concept, a metamirror is constructed capable of focusing underwater sound. Furthermore, experimental demonstrations are performed to validate the efficiency of the proposed metamirror designs. Our findings offer valuable insight for controlling acoustic fields in underwater environments and may inspire the development of related underwater acoustic devices and medical ultrasound equipment.

The microfabrication of cesium vapor cells for optically pumped magnetometry relies on optimization of buffer gas pressure in order to maximize atomic coherence time and sensitivity to external magnetic signals. We demonstrate post-bond nitrogen buffer gas pressure tuning through localized heating of an integrated micropill dispenser. We characterize the variation in the intrinsic longitudinal relaxation rate, ${\gamma }_{10}$, and magnetic sensitivity, as a function of the resulting nitrogen buffer gas pressure. Measurements are conducted by employing an optically pumped magnetometer operating in a free-induction-decay configuration. ${\gamma }_{10}$ is extracted across a range of nitrogen pressures between $60$ and $700$ torr, measuring a minimum of 140 Hz at 115 torr. In addition, we achieve sensitivities as low as 130 $\mathrm{fT}/\sqrt{\text{Hz}}$ at a bias field amplitude of $\mathrm{about}50\text{μ}\text{T}$. With the optimal nitrogen buffer gas pressure now quantified and achievable post-fabrication, these mass-producible cells can be tailored to suit a variety of sensing applications, ensuring peak magnetometer performance.

Nonreciprocal microwave routing plays a crucial role in measuring quantum circuits, and allows for realizing cascaded quantum systems for generating and stabilizing entanglement between noninteracting qubits. The most commonly used tools for implementing directionality are ferrite-based circulators. These devices are versatile, but suffer from excess loss, a large footprint, and fixed directionality. For utilizing nonreciprocity in scalable quantum circuits it is desirable to develop efficient integration of low-loss and in-situ controllable directional elements. Here, we report the design and experimental realization of a minimal controllable directional interface that can be directly coupled to superconducting qubits. In the device presented, nonreciprocity is realized through a combination of interference and phase-controlled parametric pumping. We have achieved a maximum directionality of around 30 dB, and the performance of the device is predicted quantitatively from independent calibration measurements. Using the excellent agreement of model and experiment, we predict that the circuit will be useable as a chiral qubit interface with inefficiencies at the $1\mathrm{\%}$ level or below. Our work offers a promising route for realizing high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, and provides a path for isolator-free qubit readout schemes.

Accurate thermometry of laser-cooled ions is crucial for the performance of the trapped-ion quantum computing platform. However, most existing methods face a computational exponential bottleneck. Recently, a thermometry method based on bichromatic driving was theoretically proposed by Vybornyi et al. [PRX Quantum 4, 040346 (2023)] to overcome this obstacle, which allows the computational complexity to remain constant with the increase of ion numbers. In this paper, we provide a detailed statistical analysis of this method and prove its robustness regarding several imperfect experimental conditions using Floquet theory. We then experimentally verify its good performance on a linear-segmented-surface-electrode-ion-trap platform. This method is proven to be effective from near the motional ground state to a few mean phonon numbers. Our theoretical analysis and experimental verification demonstrate that the scheme can accurately and efficiently measure the temperature in ion crystals.

Rydberg atoms as versatile tools for quantum applications are extremely sensitive to electric fields. When utilizing these atoms, it becomes imperative to comprehensively characterize and mitigate ambient electric field noise. Using single Rydberg atoms in optical tweezer arrays, we reveal that the dominant ambient electric field noise originates from electrons bound to the vacuum cell surface. These electrons are found to be generated by the 297-nm light used for single-photon Rydberg excitation. Once the electrons are effectively desorbed from the surface through exposure to ultraviolet or red light, the coherence of the ground-Rydberg transition is enhanced significantly. Furthermore, we demonstrate collective oscillations of four atoms in the full Rydberg blockade regime. Our investigations will advance the control and reliability of Rydberg-atom-based systems for various quantum technologies.

Suitably tailored forms of spatiotemporal modulation in electronic circuit networks have been recently employed to overcome fundamental challenges in modern electronic systems, including breaking reciprocity, squeezing the footprint of high-Q resonators, and overcoming the delay-bandwidth limit. Rotating patterns of temporal modulations have been used to synthesize angular momentum, which replaces magnetic bias to break reciprocity in integrated circuits. However, this approach is limited by trade-offs between modulation speed, footprint, and bandwidth of operation. Rotating switching patterns in commutated capacitor networks also enables compact filters and quasielectrostatic wave propagation, overcoming the delay-bandwidth limit. In this paper, we combine these mechanisms in an integrated-circuit ring that synthetically rotates in two dimensions, realizing an effective helicoidal motion that provides ultrabroadband quasielectrostatic nonreciprocal responses fitting within a theoretically infinitesimal size. We also analyze the impact of modulation signal noise on time-modulated nonreciprocal components and unveil the role of a dynamic noise mechanism based on which the noise level increases in the presence of a strong signal passing through the component, along with methods to mitigate this effect. We experimentally verify these principles in a three-port integrated circulator based on a 65-nm CMOS process that operates from dc to 1 GHz with a miniaturization factor of 2 × ${10}^6$.

The reference-frame-independent quantum key distribution (RFI QKD) protocol enables QKD systems to function effectively despite slowly varying reference frames, offering a distinct advantage in practical scenarios, particularly in mobile platforms. In this study, we successfully distribute secure key bits over a 250-km optical fiber distance by developing an RFI QKD system with a repetition rate of 150 MHz. Benefiting from high repetition rate, we achieve a finite-key secret key rate of 49.65 bit/s at a distance of 200 km, which is more than 3 times higher than state-of-the-art systems. Our work dramatically extends the transmission distance and enhances the secret key rate of RFI QKD, significantly promoting its practical application.

The nonreciprocal supercurrent phenomenon, known as the superconducting-diode effect (SDE), has garnered great attention because of its immense potential for future nondissipative quantum devices. Here, we demonstrate lateral inversion-symmetry breaking generated by the asymmetric thickness for the realization of the SDE in a stepped ${\mathrm{NbSe}}_2$ nanoflake, which eliminates the need for complex conventional heterostructures or epitaxial structures. The electrical measurements and theoretical calculations reveal a robust SDE efficiency of up to 22.6%, primarily attributed to the presence of lateral inversion-symmetry-breaking-induced asymmetric vortex entry. Our findings emphasize the universality and effective control of vortices in achieving SDEs, and open alternative avenues for advancing the application of SDEs in van der Waals superconductors.

The demand for high-density memory drives the development of multistate nonvolatile memory devices. However, switching to an assigned intermediate memory state requires additional steps in multistate memories such as ferroelectric tunnel junctions (FTJs). Here, we design in-plane FTJs by utilizing ferroelectric control of the metal-semiconductor transition in α-tellurene$/{\mathrm{In}}_2{\mathrm{Se}}_3$ van der Waals heterostructures. The tunnel electroresistance ratio of in-plane FTJs exhibits more pronounced differences in two transport directions with the increase in channel length, and it can remain above 5 × ${10}^4$% at low bias voltage. Furthermore, synergistic anisotropic transport and ferroelectric polarization can induce four independent storage states, enabling direct switching between the four states without requiring the erasing step. This work simplifies operations and offers an alternative approach for implementing multistate nonvolatile memory.

Our study aims to increase the spatial resolution of high-sensitivity magnetometry based on singlet-transition infrared (IR) absorption using nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond in monolithic cavities, with potential applications in biomagnetic field detection. We develop a master-equation treatment of optically detected magnetic resonance, incorporating IR light saturation effects. This master equation provides the singlet population, which is then utilized to calculate the reflectivity and ultimately derive the magnetic field sensitivity taking into account photon and spin shot noise. We further show that our model is compatible with experiments of IR-based $\mathrm{N}$-$V$-center magnetometry. Through optimization in a high-parameter space, we uncover the potential to achieve sensitivities in the order of subpicotesla, even for submillimeter scales.

The silicon T center’s narrow, telecommunications-band optical emission, long spin coherence, and direct photonic integration have spurred interest in this emitter as a spin-photon interface for distributed quantum computing and networking. However, key parameters of the T center’s spin-selective optical transitions remain undetermined or ambiguous in the literature. In this paper, we present a Hamiltonian of the T center TX state and determine key parameters of the optical transition from ${\mathrm{T}}_0$ to ${\mathrm{TX}}_0$ from a combined analysis of published results, density functional theory, and new spectroscopy. We resolve ambiguous values of the internal defect potential in the literature, and we present the first measurements of electrically tuned T center emission. As a result, we provide a model of the T center’s optical and spin properties under strain, electric, and magnetic fields that can be utilized for realizing quantum technologies.

Radio-frequency (rf) receivers using Rydberg atoms offer appealing features over classical sensors, such as their size, frequency tuning range, and lack of field absorption. In this work, we extend the application space by demonstrating a Rydberg atom rf polarimeter. Using rf heterodyne with three independent and orthogonal local oscillators, we are able to extract the polarization ellipse of the field in three dimensions, in addition to the total amplitude of the field. We use the relative phases and amplitudes of the three generated heterodyne signals to measure the field amplitudes and phases along three cardinal axes giving the full three-dimensional polarization. We demonstrate this polarization measurement for incoming fields at different angles around the sensor. Lastly, we investigate the reception of data symbols encoded in the horizontal and vertical signal field polarizations and the phase between them. Our measurements yield an amplitude noise of $57\text{μ}\mathrm{V}/\mathrm{m}/\sqrt{\text{Hz}}$ for horizontal polarization, $66\text{μ}\mathrm{V}/\mathrm{m}/\sqrt{\text{Hz}}$ for vertical polarization, and a standard deviation of 0.094 rad in the phase between the field components.

The Laser Interferometer Space Antenna (LISA) senses gravitational waves by measuring distance fluctuations between three spacecraft (SCs). These measurements rely on precise tracking of a beat-note phase that is formed on a quadrant photodiode (QPD) at each SC by interference of a local laser with a laser sent from a distant SC. The crucial prerequisite of the phase tracking is a successful acquisition of the beat-note frequency. This paper aims to optimize the carrier-to-noise density ratio (CNR) during this process and to evaluate the resulting probability of detection (PD). The CNR is generally lowest during the beat-note acquisition process, since the pointing accuracy relies on coarse acquisition techniques. Based on analytical models, we examine which combinations of QPD segments for the signal readout yield the highest CNR, i.e., are least susceptible to pointing errors. We find from simulations that the highest CNR is ensured by taking the maximum of a combination of two segments in the vertical and horizontal directions. For pointing errors ($3\sigma$) of $3.9\text{μ}\text{rad}$ and $4.3\text{μ}\text{rad}$, this yields an improvement of around 3.7 dB and 5.6 dB in the CNR, respectively, in comparison to a combination of all four segments. In addition, the PD for various configurations of the baselined Fourier-peak detection is analyzed. Here, we find that the PD is most sensitive to the CNR compared to the design parameters of the acquisition scheme, in particular the FFT length. Moreover, it is shown that the aforementioned improvements in the CNR can lead to a significant enhancement of the PD.