Explore the vast range of titles available.

Phonons are considered to be universal quantum transducers due to their ability to couple to a wide variety of quantum systems. Among these systems, solid-state point defect spins are known for being long-lived optically accessible quantum memories. Recently, it has been shown that inversion-symmetric defects in diamond, such as the negatively charged silicon vacancy center (SiV), feature spin qubits that are highly susceptible to strain. Here, we leverage this strain response to achieve coherent and low-power acoustic control of a single SiV spin, and perform acoustically driven Ramsey interferometry of a single spin. Our results demonstrate an efficient method of spin control for these systems, offering a path towards strong spin-phonon coupling and phonon-mediated hybrid quantum systems. Qubits in solid state systems like point defects in diamond can be influenced by local strain. Here the authors use surface acoustic waves to coherently control silicon vacancies in diamond, which have the potential to reach the strong coupling regime necessary for many applications.

High-power continuous-wave (CW) lasers are used in a variety of areas including industry, medicine, communications, and defense. Yet, conventional optics, which are based on multi-layer coatings, are damaged when illuminated by high-power CW laser light, primarily due to thermal loading. This hampers the effectiveness, restricts the scope and utility, and raises the cost and complexity of high-power CW laser applications. Here we demonstrate monolithic and highly reflective mirrors that operate under high-power CW laser irradiation without damage. In contrast to conventional mirrors, ours are realized by etching nanostructures into the surface of single-crystal diamond, a material with exceptional optical and thermal properties. We measure reflectivities of greater than 98% and demonstrate damage-free operation using 10 kW of CW laser light at 1070 nm, focused to a spot of 750 μm diameter. In contrast, we observe damage to a conventional dielectric mirror when illuminated by the same beam. Our results initiate a new category of optics that operate under extreme conditions, which has potential to improve or create new applications of high-power lasers. Mirrors that demonstrate 98% reflectivity and withstand 10 kilowatts of focused continuous-wave laser light are created by nanoscale fabrication of single-crystal diamond. The work finds applications in medicine, defence, industry, and communications.

The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. For quantum bits in the solid state, decoherence from thermal vibrations of the surrounding lattice can typically only be suppressed by lowering the temperature of operation. Here, we use a nano-electro-mechanical system to mitigate the effect of thermal phonons on a spin qubit – the silicon-vacancy colour centre in diamond – without changing the system temperature. By controlling the strain environment of the colour centre, we tune its electronic levels to probe, control, and eventually suppress the interaction of its spin with the thermal bath. Strain control provides both large tunability of the optical transitions and significantly improved spin coherence. Finally, our findings indicate the possibility to achieve strong coupling between the silicon-vacancy spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics. Silicon-vacancy centres in diamond are promising candidates as emitters in photonic quantum networks, but their coherence is degraded by large electron-phonon interactions. Sohn et al. demonstrate the use of strain to tune a silicon vacancy’s electronic structure and suppress phonon-mediated decoherence.

Single-crystal diamond, with its unique optical, mechanical and thermal properties, has emerged as a promising material with applications in classical and quantum optics. However, the lack of heteroepitaxial growth and scalable fabrication techniques remains the major limiting factors preventing more wide-spread development and application of diamond photonics. In this work, we overcome this difficulty by adapting angled-etching techniques, previously developed for realization of diamond nanomechanical resonators, to fabricate racetrack resonators and photonic crystal cavities in bulk single-crystal diamond. Our devices feature large optical quality factors, in excess of 10 5 , and operate over a wide wavelength range, spanning visible and telecom. These newly developed high-Q diamond optical nanocavities open the door for a wealth of applications, ranging from nonlinear optics and chemical sensing, to quantum information processing and cavity optomechanics. Single-crystal diamond is a promising material for applications in classical and quantum optics, but the lack of scalable fabrication remains an issue. Here, Burek et al . adapt angle-etching nanofabrication techniques to realize ring resonators and photonic crystal cavities in single crystal diamond with quality factors in excess of 10 5 .

Modern computing and communication technologies such as supercomputers and the Internet are based on optically connected networks of microwave-frequency information processors. An analogous architecture has been proposed for quantum networks, using optical photons to distribute entanglement between remote superconducting quantum processors. Here we report a step towards such a network by observing non-classical correlations between photons in an optical link and a superconducting quantum device. We generate these states of light through a spontaneous parametric down-conversion process in a chip-scale piezo-optomechanical transducer, and we measure a microwave–optical cross-correlation exceeding the Cauchy–Schwarz classical bound for thermal states. As further evidence of the non-classical character of the microwave–optical photon pairs, we observe antibunching in the microwave state conditioned on detection of an optical photon. Such a transducer can be readily connected to an independent superconducting qubit module and serve as a key building block for optical quantum networks of microwave-frequency qubits. A transducer that generates microwave–optical photon pairs is demonstrated. This could provide an interface between optical communication networks and superconducting quantum devices that operate at microwave frequencies.

Realization of physical systems for quantum information processing fundamentally rests on the ability to generate entanglement among many quantum bits. To this end, solid state quantum systems are often considered a scalable approach due to the relative ease of generating of a large number of individual qubits. However, realizing strong coherent interactions that dominate decoherence processes in the solid state environment is a formidable challenge that has continued to motivate the investigation of new physical systems to store quantum information and new mechanisms to achieve controllable interactions. This thesis takes steps in these directions with diamond color centers, which can store optically accessible quantum information in their electronic spin. We study color center spins as acoustic two level systems, and consider whether their interaction with single phonons in diamond can be engineered to be coherent. Through spectroscopy of color centers in diamond nanomechanical devices and follow-up theoretical work, we identify the negatively charged silicon vacancy (SiV) color center as a promising candidate for phonon-mediated quantum information processing. In the process, an electromechanical device platform capable of tuning the strain environment of color centers is developed. It is used to mitigate thermal decoherence of the SiV spin and demonstrate photon-mediated quantum interference between two SiV centers on a diamond chip, highlighting the utility of nanomechanical devices for photonic quantum networks. Finally, we present high quality factor, wavelength scale acoustic resonators in diamond using phononic crystals towards a coherent interface between SiV centers and single phonons.

The performance of superconducting quantum circuits is primarily limited by dielectric loss due to interactions with two-level systems (TLS). State-of-the-art circuits with engineered material interfaces are approaching a limit where dielectric loss from bulk substrates plays an important role. However, a microscopic understanding of dielectric loss in crystalline substrates is still lacking. In this work, we show that boron acceptors in silicon constitute a strongly coupled TLS bath for superconducting circuits. We discuss how the electronic structure of boron acceptors leads to an effective TLS response in silicon. We sweep the boron concentration in silicon and demonstrate the bulk dielectric loss limit from boron acceptors. We show that boron-induced dielectric loss can be reduced in a magnetic field due to the spin-orbit structure of boron. This work provides the first detailed microscopic description of a TLS bath for superconducting circuits, and demonstrates the need for ultrahigh purity substrates for next-generation superconducting quantum processors.

Coherent transduction of quantum states from the microwave to the optical domain can play a key role in quantum networking and distributed quantum computing. We present the design of a piezo-optomechanical device formed in a hybrid lithium niobate on silicon platform, that is suitable for microwave-to-optical quantum transduction. Our design is based on acoustic hybridization of an ultra-low mode volume piezoacoustic cavity with an optomechanical crystal cavity. The strong piezoelectric nature of lithium niobate allows us to mediate transduction via an acoustic mode which only minimally interacts with the lithium niobate, and is predominantly silicon-like, with very low electrical and acoustic loss. We estimate that this transducer can realize an intrinsic conversion efficiency of up to 35% with <0.5 added noise quanta when resonantly coupled to a superconducting transmon qubit and operated in pulsed mode at 10 kHz repetition rate. The performance improvement gained in such hybrid lithium niobate-silicon transducers make them suitable for heralded entanglement of qubits between superconducting quantum processors connected by optical fiber links.

Entangling microwave and optical photons is one of the promising ways to realize quantum transduction through quantum teleportation. This paper investigates the entanglement of microwave-optical photon pairs generated from an electro-optomechanical system driven by a blue-detuned pulsed Gaussian pump. The photon pairs are obtained through weak parametric-down-conversion, and their temporal correlation is revealed by the second-order correlation function. We then study the discrete variable entanglement encoded in the time bin degree of freedom, where entanglement is identified by Bell inequality violation. Furthermore, we estimate the laser-induced heating and show that the pulse-pumped system features lower heating effects while maintaining a reasonable coincidence photon counting rate.

Optomechanical crystals (OMCs) enable coherent interactions between optical photons and microwave acoustic phonons, and represent a platform for implementing quantum transduction between microwave and optical signals. Optical absorption-induced thermal noise at cryogenic (millikelvin) temperatures is one of the primary limitations of performance for OMC-based quantum transducers. Here, we address this challenge with a two-dimensional silicon OMC resonator that is side-coupled to a mechanically detached optical waveguide, realizing a six-fold reduction in the heating rate of the acoustic resonator compared to prior state-of-the-art, while operating in a regime of high optomechanical-backaction and millikelvin base temperature. This reduced heating translates into a demonstrated phonon-to-photon conversion efficiency of 93.1 \\(\\pm\\) 0.8% at an added noise of 0.25 \\(\\pm\\) 0.01 quanta, representing a significant advance toward quantum-limited microwave-optical frequency conversion and optically-controlled quantum acoustic memories.