Signatures of discrete time crystalline order in dissipative spin ensembles

Discrete time-translational symmetry in a periodically driven many-body system can be spontaneously broken to form a discrete time crystal, an exotic new phase of matter. We present observations characteristic of discrete time crystalline order in a driven system of paramagnetic P-donor impurities in isotopically enriched 28Si cooled below 10 K. The observations exhibit a stable subharmonic peak at half the drive frequency which remains pinned even in the presence of pulse error, a signature of discrete time crystalline order. This signal has a finite lifetime of ∼ 100 Floquet periods, but this effect is long-lived relative to coherent spin–spin interaction timescales, lasting ∼ 104 times longer.We present simulations of the system based on the paradigmatic central spin model and show good agreement with experiment. We investigate the role of dissipation and interactions within this model, and show that both are capable of giving rise to discrete time crystal-like behaviour

Maser threshold characterization by resonator Q-factor tuning

Whereas the laser is nowadays an ubiquitous technology, applications for its microwave analog, the maser, remain highly specialized, despite the excellent low-noise microwave amplification properties. The widespread application of masers is typically limited by the need of cryogenic temperatures. The recent realization of a continuous-wave room-temperature maser, using NV− centers in diamond, is a first step towards establishing the maser as a potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating space of a maser using NV− centers. We focus on the interplay of two key parameters for emission of microwave photons: the quality factor of the microwave resonator and the degree of spin level-inversion. We characterize the performance of the maser as a function of these two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission

Coupling microwave photons to topological spin textures in Cu2OSeO3

Topologically protected nanoscale spin textures, known as magnetic skyrmions, possess particlelike properties and feature emergent magnetism effects. In bulk cubic helimagnets, distinct skyrmion resonant modes are already identified using a technique such as ferromagnetic resonance in spintronics. However, direct light-matter coupling between microwave photons and skyrmion resonance modes still needs to be demonstrated. Utilizing two distinct cavity systems, we observe a direct interaction between the cavity resonant mode and two resonant skyrmion modes, the counterclockwise gyration and breathing modes, in bulk Cu 2 OSeO 3 . For both resonant modes, we find the largest coupling strength at 57 K indicated by an enhancement of the cavity linewidth at the degeneracy point. We study the effective coupling strength as a function of temperature within the expected skyrmion phase. We attribute the maximum in effective coupling strength to the presence of a large number of skyrmions, and correspondingly to a completely stable skyrmion lattice. Our experimental findings indicate that the coupling between photons and resonant modes of magnetic skyrmions depends on the relative density of these topological particles instead of the pure spin number in the system

Strain in heterogeneous quantum devices with atomic layer deposition

Abstract We investigated the use of dielectric layers produced by atomic layer deposition (ALD) as an approach to strain mitigation in composite silicon/superconductor devices operating at cryogenic temperatures. We show that the addition of an ALD layer acts to reduce the strain of spins closest to silicon/superconductor interface where strain is highest. We show that appropriately biasing our devices at the hyperfine clock transition of bismuth donors in silicon, we can remove strain broadening and that the addition of ALD layers left T 2 (or temporal inhomogeneities) unchanged in these natural silicon devices.</jats:p

Near-Surface Te+ 125 Spins with Millisecond Coherence Lifetime

Impurity spins in crystal matrices are promising components in quantum technologies, particularly if they can maintain their spin properties when close to surfaces and material interfaces. Here, we investigate an attractive candidate for microwave-domain applications, the spins of group-VI Te+125 donors implanted into natural Si at depths as shallow as 20 nm. We show that surface band bending can be used to ionize such near-surface Te to spin-active Te+ state, and that optical illumination can be used further to control the Te donor charge state. We examine spin activation yield, spin linewidth, and relaxation (T1) and coherence times (T2) and show how a zero-field 3.5 GHz "clock transition"extends spin coherence times to over 1 ms, which is about an order of magnitude longer than other near-surface spin systems

High-Cooperativity Coupling of a Rare-Earth Spin Ensemble to a Superconducting Resonator Using Yttrium Orthosilicate as a Substrate

Yttrium orthosilicate ( Y 2 Si O 5 , or YSO) has proved to be a convenient host for rare-earth ions used in demonstrations of microwave quantum memories and optical memories with microwave interfaces and shows promise for coherent microwave-optical conversion owing to its favorable optical and spin properties. The strong coupling required by such microwave applications could be achieved using superconducting resonators patterned directly on Y 2 Si O 5 and hence we investigate here the use of Y 2 Si O 5 as an alternative to sapphire or silicon substrates for superconducting-hybrid-device fabrication. A Nb N resonator with frequency 6.008 GHz and low-power quality factor Q ≈ 400 000 is fabricated on a Y 2 Si O 5 substrate doped with isotopically enriched 145 Nd . Measurements of dielectric loss yield a loss tangent tan  δ = 4 × 10 − 6 , comparable to that of sapphire. Electron spin resonance (ESR) measurements performed using the resonator show the characteristic angular dependence expected from the anisotropic 145 Nd spin and the coupling strength between the resonator and the electron spins is in the high-cooperativity regime ( C = 30 ). These results demonstrate that Y 2 Si O 5 is an excellent substrate for low-loss, high- Q microwave resonators, especially in applications for coupling to optically accessible rare-earth spins

Quantum Engineering With Hybrid Magnonic Systems and Materials (Invited Paper)

Quantum technology has made tremendous strides over the past two decades with remarkable advances in materials engineering, circuit design, and dynamic operation. In particular, the integration of different quantum modules has benefited from hybrid quantum systems, which provide an important pathway for harnessing different natural advantages of complementary quantum systems and for engineering new functionalities. This review article focuses on the current frontiers with respect to utilizing magnons for novel quantum functionalities. Magnons are the fundamental excitations of magnetically ordered solid-state materials and provide great tunability and flexibility for interacting with various quantum modules for integration in diverse quantum systems. The concomitant-rich variety of physics and material selection enable exploration of novel quantum phenomena in materials science and engineering. In addition, the ease of generating strong coupling with other excitations makes hybrid magnonics a unique platform for quantum engineering. We start our discussion with circuit-based hybrid magnonic systems, which are coupled with microwave photons and acoustic phonons. Subsequently, we focus on the recent progress of magnon–magnon coupling within confined magnetic systems. Next, we highlight new opportunities for understanding the interactions between magnons and nitrogen-vacancy centers for quantum sensing and implementing quantum interconnects. Lastly, we focus on the spin excitations and magnon spectra of novel quantum materials investigated with advanced optical characterization

Towards high performance dielectric microwave resonators for X-band EPR spectroscopy

Microwave (MW) resonators in Electron Paramagnetic Resonance (EPR) spectroscopy concentrate the MW magnetic field (B1) at the sample and separate the MW electric field from the sample. There are numerous experimental methods in EPR spectroscopy which all impose different requirements on MW resonators (e.g. high or low quality factor, MW conversion, and B1-field homogeneity). Although commercial spectrometers offer standardized MW resonators for a broad application range, newly emerging and highly-specialized research fields push these spectrometers to or beyond their sensitivity limits. Optimizing the MW resonator offers one direct approach to improve the sensitivity. Here we present three low-cost optimization approaches for a commercially available X-band (9–10 GHz) MW resonator for three experimental purposes (continuous-wave (CW), transient and pulse EPR). We obtain enhanced MW conversion factors for all three optimized resonators and higher quality factors for two optimized resonators. The latter is important for CW and transient EPR. Furthermore, we fabricated a resonator which features an extended area of homogeneous B1-field and, hence, improved pulse EPR performance. Our results demonstrate that small changes to a commercial MW resonator can enhance its performance in general or for specific applications

Tuning high-Q superconducting resonators by magnetic field reorientation

ABSTRACT Superconducting resonators interfaced with paramagnetic spin ensembles are used to increase the sensitivity of electron spin resonance experiments and are key elements of microwave quantum memories. Certain spin systems that are promising for such quantum memories possess “sweet spots” at particular combinations of magnetic fields and frequencies, where spin coherence times or linewidths become particularly favorable. In order to be able to couple high-Q superconducting resonators to such specific spin transitions, it is necessary to be able to tune the resonator frequency under a constant magnetic field amplitude. Here, we demonstrate a high-quality, magnetic field resilient superconducting resonator, using a 3D vector magnet to continuously tune its resonance frequency by adjusting the orientation of the magnetic field. The resonator maintains a quality factor of >10^{5} up to magnetic fields of 2.6 T, applied predominantly in the plane of the superconductor. We achieve a continuous tuning of up to 30 MHz by rotating the magnetic field vector, introducing a component of 5 mT perpendicular to the superconductor

Echo trains in pulsed electron spin resonance of a strongly coupled spin ensemble

We report on a novel dynamical phenomenon in electron spin resonance experiments of phosphorus donors. When strongly coupling the paramagnetic ensemble to a superconducting lumped element resonator, the coherent exchange between these two subsystems leads to a train of periodic, self-stimulated echos after a conventional Hahn echo pulse sequence. The presence of these multi-echo signatures is explained using a simple model based on spins rotating on the Bloch sphere, backed up by numerical calculations using the inhomogeneous Tavis-Cummings Hamiltonian