By leveraging tunable diode lasers and a synergetic combination of public and private investments and partnerships, the industry can speed development and adoption of photonic integrated circuit (PIC) technologies for the emerging quantum market.

The second quantum revolution, Quantum 2.0, is fueled by recent progress in generating and manipulating quantum states in both light and matter, leading to new applications such as quantum sensing, computing, and communications. These new applications, which leverage unique quantum properties, such as superposition, entanglement, and measurement sensitivity of quantum states to offer fundamental advantages over classical technologies, are in principle enabled by the Quantum 1.0 technologies such as lasers. As quantum information science and technology progresses steadily from a purely academic discipline towards technology demonstrations, the imperative to transition from laboratory -grade lasers to industry -grade lasers becomes evident in the quest for scalability, robustness, improved performance, and often, reduced SWaP (Size, Weight, and Power) for field deployability. This paper provides an overview of the current state and challenges of laser - enabled quantum applications and outlines the advancements in laser technologies from macro -optics to micro -optics to integrated photonics with their prospects towards the practical realization of quantum advantage.

Hexagonal sodium yttrium fluoride (β-NaYF) is a promising material for optical refrigeration due to the narrow crystal field splitting of the Yb(III) ion. However, growing single crystals of β-NaYF remains a challenge due to thermal expansion stresses during melt growth. We demonstrate a hydrothermal synthesis of β-NaYF with widely tunable aspect ratios that match computationally predicted cavity resonances. The β-NaYF microcrystals contain 10% Yb(III) cations and are used to build optomechanical laser-refrigeration cantilever devices. Laser refrigeration of these devices shows cooling up to 12.5°C, which is measured using the cantilever’s fundamental eigenfrequency and photoluminescence from the Yb(III) ions.

Hexagonal sodium yttrium fluoride with Na3xY2-xF6 stoichiometry (beta-NaYF) is a promising material for luminescence upconversion applications due to the narrow crystal field splitting of the Yb(III) ion's lower F-2(7/)2 manifold. However, growing single crystals of beta-NaYF remains an outstanding challenge due to thermal expansion stresses that cause cracking during melt growth. In this paper, we demonstrate a novel hydrothermal synthesis of beta-NaYF with the ability to tune the aspect ratio from microplatelets to microrods with aspect ratios that match computationally predicted cavity (Mie) resonances. These crystals have a root-mean-square roughness below 1 nm after calcination, which makes them ideal for optical cavities. The beta-NaYF microcrystals are doped with 10% Yb(III) cations and are used to build optomechanical laser-refrigeration devices consisting of a hexagonal beta-NaYF crystal located at the end of a cantilever. Laser refrigeration of these devices by >12.5 degrees C is observed using calibrated measurements of both the cantilever's fundamental eigenfrequency and a Boltzmann fit to crystal field luminescence from the Yb(III) ions.

In this work, bulk graphene-doped YBa2Cu3O7-delta(YBCO) high-temperature superconductor samples were pre-pared with composition of YBCO + x wt.% graphene nanoplatelets (G) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The X-ray diffraction patterns show the YBCO orthorhombic phase in all the samples. The SEM images show good grain connectivity between YBCO grains in graphene-doped samples. Furthermore, the broadening of resistivity under applied magnetic fields up to 9T and thermally activated flux creep in the mixed state were studied using Arrhenius plots. The activation energy U0 (H) increased with graphene doping results in better flux pinning and higher critical current densities. Moreover, improvement in the critical temperature (TC), upper critical field (mu 0HC2) and the irreversibility field (mu 0Hirr) were observed in graphene-doped samples as compared to the pure YBCO sample.

Quantum information science and technology (QIST) is a critical and emerging technology with the potential for enormous world impact and is currently invested in by over 40 nations. To bring these large-scale investments to fruition and bridge the lower technology readiness levels (TRLs) of fundamental research at universities to the high TRLs necessary to realize the promise of practical quantum advantage accessible to industry and the public, we present a roadmap for Quantum Technology Demonstration Projects (QTDPs). Such QTDPs, focused on intermediate TRLs, are large-scale public-private partnerships with a high probability of translation from laboratory to practice. They create technology demonstrating a clear 'quantum advantage' for science breakthroughs that are user-motivated and will provide access to a broad and diverse community of scientific users. Successful implementation of a program of QTDPs will have large positive economic impacts.

Over the last decade there have been many advances in studies of quantum walks (QWs) including a momentum-space QW recently realized in our spinor Bose-Einstein condensate system. This QW possessed behaviors that generally agreed with theoretical predictions; however, it also showed momentum distributions that were not adequately explained by the theory. We present a theoretical model which proves that the coherent dynamics of the spinor condensate is sufficient to explain the experimental data without invoking the presence of a thermal cloud of atoms as in the original theory. Our numerical findings are supported by an analytical prediction for the momentum distributions in the limit of zero-temperature condensates. This current model provides more complete explanations to the momentum-space QWs that can be applied to study quantum search algorithms and topological phases in Floquet-driven systems.

Optically levitated nanoparticles provide excellent systems to sense minute forces and explore quantum effects in a large system. However, optically levitated nanoparticles are prone to heating and require cooling and temperature stabilization to reach sensitivities necessary to study small forces and quantum effects. This problem can be solved by trapping nanocrystals doped with rare-earth ions that can be anti-Stokes cooled by tens of degrees. The efficiency of the anti-Stokes depends on gas pressure and can counter heating due to optical absorption. Cooling nanocrystals allows for thermally stabilizing nanocrystal systems to measure minute forces and quantum effects.

We have realized a quantum walk in momentum space with a rubidium spinor Bose-Einstein condensate by applying a periodic kicking potential as a walk operator and a resonant microwave pulse as a coin toss operator. The generated quantum walks appear to be stable for up to ten steps and then quickly transit to classical walks due to spontaneous emissions induced by laser beams of the walk operator. We investigate these quantum to classical walk transitions by introducing well-controlled spontaneous emissions with an external light source during quantum walks. Our findings demonstrate a scheme to control the robustness of the quantum walks and can also be applied to other cold atom experiments involving spontaneous emissions.

Laser refrigeration of rare-earth doped optically levitated nanoparticles allows for cooling of 42 K. Cooling is calibrated using a cryostat. Cooling efficiency decreases at pressures below 5 mbar as thermal contact with gas molecules decreases.

Magnetic and thermal microscopy can be performed concurrently to probe physical performance of integrated circuits. We present wide-field imaging of current-induced magnetic and thermal patterns using optically-detected magnetic resonance of NV − centers in nanodiamond ensembles.

The negatively-charged nitrogen vacancy (NV$^-$) centre in diamond is a remarkable optical quantum sensor for a range of applications including, nanoscale thermometry, magnetometry, single photon generation, quantum computing, and communication. However, to date the performance of these techniques using NV$^-$ centres has been limited by the thermally-induced spectral wandering of NV$^-$ centre photoluminescence due to detrimental photothermal heating. Here we demonstrate that solid-state laser refrigeration can be used to enable rapid (ms) optical temperature control of nitrogen vacancy doped nanodiamond (NV$^-$:ND) quantum sensors in both atmospheric and \textit{in vacuo} conditions. Nanodiamonds are attached to ceramic microcrystals including 10\% ytterbium doped yttrium lithium fluoride (Yb:LiYF$_4$) and sodium yttrium fluoride (Yb:NaYF$_4$) by van der Waals bonding. The fluoride crystals were cooled through the efficient emission of upconverted infrared photons excited by a focused 1020 nm laser beam. Heat transfer to the ceramic microcrystals cooled the adjacent NV$^-$:NDs by 10 and 27 K at atmospheric pressure and $\sim$10$^{-3}$ Torr, respectively. The temperature of the NV$^-$:NDs was measured using both Debye-Waller factor (DWF) thermometry and optically detected magnetic resonance (ODMR), which agree with the temperature of the laser cooled ceramic microcrystal. Stabilization of thermally-induced spectral wandering of the NV$^{-}$ zero-phonon-line (ZPL) is achieved by modulating the 1020 nm laser irradiance. The demonstrated cooling of NV$^-$:NDs using an optically cooled microcrystal opens up new possibilities for rapid feedback-controlled cooling of a wide range of nanoscale quantum materials.

Solid state laser refrigeration can cool optically levitated nanocrystals in an optical dipole trap, allowing for internal temperature control by mitigating photothermal heating. This work demonstrates cooling of ytterbium-doped cubic sodium yttrium fluoride nanocrystals to 252 K on average with the most effective crystal cooling to 241 K. The amount of cooling increases linearly with the intensity of the cooling laser and is dependent on the pressure of the gas surrounding the nanocrystal. Cooling optically levitated nanocrystals allows for crystals prone to heating to be studied at lower pressures than currently achievable and for temperature control and stabilization of trapped nanocrystals.

Siamak Dadras,1, 2 Robert M. Pettit,3 Danika R. Luntz-Martin,2, 4 Kewen Xiao,5 M. Bhattacharya,2, 5 and A. Nick Vamivakas1, 2, 4, ∗ The Institute of Optics, University of Rochester, Rochester, NY 14627, USA Center for Coherence and Quantum Optics, University of Rochester, Rochester, NY 14627, USA Institute for Research in Electronics and Applied Physics, and Joint Quantum Institute, University of Maryland, College Park, MD 20742, USA Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA School of Physics and Astronomy, Rochester Institute of Technology, Rochester, NY 14623, USA

We present theoretical and experimental investigations of higher order correlations of mechanical motion in the recently demonstrated optical tweezer phonon laser, consisting of a silica nanosphere trapped in vacuum by a tightly focused optical beam [R. M. Pettit et al., Nature Photonics 13, 402 (2019)]. The nanoparticle phonon number probability distribution is modeled with the master equation formalism in order to study its evolution across the lasing threshold. Up to fourth-order equal-time correlation functions are then derived from the probability distribution. Subsequently, the master equation is transformed into a nonlinear quantum Langevin equation for the trapped particle's position. This equation yields the non-equal-time correlations, also up to fourth order. Finally, we present experimental measurements of the phononic correlation functions, which are in good agreement with our theoretical predictions. We also compare the experimental data to existing analytical Ginzburg-Landau theory where we find only a partial match.

We report on the injection locking of an optically levitated nanomechanical oscillator (a silica nanosphere) to resonant intensity modulations of an external optical signal. We explore the characteristic features of injection locking in this system, e.g. the phase pull-in effect and the injection-induced reduction of the oscillation linewidth. Our measurements are in good agreement with theoretical predictions and deepen the analogy of injection locking in levitated optomechanical systems to that in optical systems (lasers). By measuring the force noise of our feedback cooled free-running oscillator, we attain a force sensitivity of ∼23 zN/√(Hz). This can readily allow, in fairly short integration times, for tests of violations of Newtonian gravity and searching for new small-scale forces. As a proof of concept, we show that the injection locking can be exploited to measure the forces optically induced on levitated nanoparticles, with potential applications in explorations of optical binding and entanglement between optically coupled nanomechanical oscillators.

Cooling of solid-state quantum emitters is crucial in quantum network applications. We present electron-spin-resonance-based thermometry of NV − center quantum emitters in nanodiamonds, cooled via laser refrigeration of their Yb3+:NaYF4 substrate.

Doping of two-dimensional (2D) semiconductors has been intensively studied toward modulating their electrical, optical, and magnetic properties. While ferromagnetic 2D semiconductors hold promise for future spintronics and valleytronics, the origin of ferromagnetism in 2D materials remains unclear. Here, we show that substitutional Fe-doping of MoS2and WS2monolayers induce different magnetic properties. The Fe-doped monolayers are directly synthesized via chemical vapor deposition. In both cases, Fe substitutional doping is successfully achieved, as confirmed using scanning transmission electron microscopy. While both Fe:MoS2and Fe:WS2show PL quenching and n-type doping, Fe dopants in WS2monolayers are found to assume deep-level trap states, in contrast to the case of Fe:MoS2, where the states are found to be shallow. Usingμm- and mm-precision local NV-magnetometry and superconducting quantum interference device, we discover that, unlike MoS2monolayers, WS2monolayers do not show a magnetic phase transition to ferromagnetism upon Fe-doping. The absence of ferromagnetism in Fe:WS2is corroborated using density functional theory calculations.

Two-dimensional semiconductors, including transition metal dichalcogenides, are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Previous efforts to form two-dimensional dilute magnetic semiconductors utilized extrinsic doping techniques or bulk crystal growth, detrimentally affecting uniformity, scalability, or Curie temperature. Here, we demonstrate an in situ substitutional doping of Fe atoms into MoS 2 monolayers in the chemical vapor deposition growth. The iron atoms substitute molybdenum sites in MoS 2 crystals, as confirmed by transmission electron microscopy and Raman signatures. We uncover an Fe-related spectral transition of Fe:MoS 2 monolayers that appears at 2.28 eV above the pristine bandgap and displays pronounced ferromagnetic hysteresis. The microscopic origin is further corroborated by density functional theory calculations of dipole-allowed transitions in Fe:MoS 2 . Using spatially integrating magnetization measurements and spatially resolving nitrogen-vacancy center magnetometry, we show that Fe:MoS 2 monolayers remain magnetized even at ambient conditions, manifesting ferromagnetism at room temperature.