Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P07: Quantum Measurement and Sensing IFocus
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Sponsoring Units: DQI Chair: Mo Chen, Massachusetts Institute of Technology MIT Room: 102 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P07.00001: Quantum sensing beyond the standard quantum limit with 2D arrays of trapped ions Kevin Gilmore, Matthew Affolter, Elena Jordan, Robert J. Lewis-Swan, Diego Barberena, Athreya Shankar, Murray J Holland, Ana Maria Rey, John Jacob Bollinger Quantum sensing protocols using trapped-ions can enable detection of weak electric fields (<1 nV/m) by sensing displacements surpassing the Standard Quantum Limit (SQL) – the sensitivity achievable with a coherent state. We present experiments investigating the limits of electric field sensing via the excitation of the center-of-mass (COM) motion of 100s of ions in a 2D crystal. By coupling the mechanical motion of the ions to their spin states by way of an optical potential, the displacement of the ion crystal can be read out via the spin state [1]. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P07.00002: Spin-squeezing using optimized parametric driving Peter Groszkowski, Catherine Leroux, Luke Govia, Aashish Clerk Spin-squeezed states are desirable for meteorological applications as they allow for sensing beyond the standard quantum limit. A variety of mechanisms for generating such states have been proposed theoretically, and in some cases, realized experimentally. Nevertheless, approaches that reach the Heisenberg-limited scaling (eg. 'two-axis twist') often require elaborate experimental setups, making them difficult to realize in practice, while ones that are more experimentally viable, (eg. 'one-axis-twist') have sub-optimal scaling. In this talk we consider a parametrically driven cavity, coupled to a spin ensemble. We show that a careful control of the parametric drive detuning and amplitude can let one achieve Heisenberg-limited scaling. We also discuss the impact of dissipation on performance. Our approach is general enough to be experimentally viable in a variety of systems including spin ensembles coupled to superconducting microwave cavities (e.g. [1]), but also spins that are strain-coupled to a nanomechanical resonator (e.g. [2,3]). |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P07.00003: Detecting spin polarization in 2D MoSe2 with nitrogen vacancy centers in diamond Bo Dwyer, Trond I Andersen, Giovanni Scuri, Takashi Taniguchi, Kenji Watanabe, Philip Kim, Hongkun Park, Mikhail Lukin Since the isolation of monolayer graphene, the catalog of exfoliatable two dimensional materials has grown to include materials with a host of properties, including semiconductors, ferromagnets, and even superconductors. Of particular interest are the transition metal dichalcogenides (TMDCs), which in the monolayer limit are direct band gap semiconductors that support tightly bound excitons. Due to spin orbit coupling and a lack of inversion symmetry, spins in the two inequivalent K valleys are polarized, which has led to great interest in TMDCs for spin- and valley-tronic applications. While the spin properties of TMDCs have been studied with optical techniques, these offer limited spatial resolution and are difficult to extract quantitative values from. We report on progress towards the measurement of optically induced spin polarization in hole doped MoSe2 using nitrogen vacancy centers in diamond as nanoscale magnetic field probes. The close proximity of these sensors, coupled with available superresolution techniques, will enable nanoscale imaging and quantification of other exotic phenomena in TMDs such as the valley hall effect and imaging of Moire superlattice TMDC structures. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P07.00004: Observation of ac Photocurrent Vortices in Monolayer MoS2 Using NV Centers Paul Jerger, Brian Zhou, Kan-Heng Lee, Masaya Fukami, Fauzia Mujid, Jiwoong Park, David Awschalom Photocurrents are central to understanding the interaction of light with matter. Although widely used, transport-based detection cannot resolve the spatial distribution of photocurrents and can suffer from low photocarrier collection efficiency. We demonstrate a contact-free method to spatially resolve photocurrents using nitrogen-vacancy (NV) centers in diamond, and discover that optical excitation of MoS2 produces photocurrent vortices via the Nernst effect. We use a near-surface ensemble of NV centers to map the magnetic field profile of photocurrents in a monolayer of MoS2 transferred onto the diamond surface. By synchronizing pulsed photoexcitation with NV ac magnetometry, we perform a quantum lock-in measurement to resolve time-dependent photocurrent densities as small as 20 nA/µm. Spatiotemporal measurements reveal a photocurrent rise time dependent on the sample’s thermal properties. This work establishes a novel probe for optoelectronic phenomena, ideally suited to two-dimensional materials, for which making contacts is challenging and can alter the intrinsic material properties. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P07.00005: Electric Field Sensing Using an NV Center Under Perpendicular Magnetic Field Ziwei Qiu, Assaf Hamo, Uri Vool, Andrew Pierce, Ruolan Xue, Tony Zhou, Amir Yacoby Nitrogen-vacancy (NV) centers in diamond can sense locally both magnetic and electric fields and hence may offer unique insight into strongly correlated matter. While NV magnetic sensing is well established, NV electric sensing is not yet widely utilized. Here we explored electric field sensing using an NV in the presence of a strong magnetic field acting perpendicular to the NV axis. We use shallow NVs (~20nm below the surface) in bulk diamonds and nanotips to explore the optimal conditions for electric field sensing. Under a perpendicular field, the original spin states mix into bright and dark states. These sates hybridize with the 15N nuclear spin due to hyperfine interaction, giving rise to periodic modulations in the spin-echo signal. Surprisingly, this hyperfine coupling strength appears to be tunable by the magnitude of the perpendicular field and is linear at least up to 200G. These findings may offer a new pathway for prolonging the coherence of the nuclear spin. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P07.00006: Diamond parabolic reflectors for nanoscale quantum sensing Brendan Shields, Natascha Hedrich, Dominik Rohner, Marietta Batzer, Patrick Maletinsky The nitrogen-vacancy (NV) center in diamond is an atomic-scale atom-like system with an electronic spin that can be initialized and detected optically, making it an exceptional system for quantum sensing of magnetic phenomena requiring high field sensitivity, fine spatial resolution, quantitative imagery [1, 2]. A particularly powerful approach is to incorporate the NV sensor in a scanning probe, allowing for nanometer spatial resolution. Key challenges for such a system are to ensure high collection efficiency and NV-sample spacing below a few 10s of nm. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P07.00007: Extending the quantum coherence of a near-surface qubit by coherently driving the paramagnetic surface environment Dolev Bluvstein, Zhiran Zhang, Claire McLellan, Nicolas Ryan Williams, Ania Jayich Surfaces enable useful functionalities for quantum systems, e.g., as interfaces to sensing targets, but often result in surface-induced decoherence where unpaired electron spins are common culprits. Here we show that the coherence time of a near-surface qubit is increased by coherent radio-frequency driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV) center as a model qubit [1]. This technique is complementary to other methods of suppressing decoherence and, importantly, requires no additional materials processing or control of the qubit. Further, by combining driving with the increased magnetic susceptibility of the double-quantum basis, we realize an overall fivefold sensitivity enhancement in NV magnetometry. Informed by our results, we discuss a path toward relaxation-limited coherence times for near-surface NV centers. The surface-spin driving technique presented here is broadly applicable to a wide variety of qubit platforms afflicted by surface-induced decoherence. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P07.00008: Observation of a quantum phase from classical rotation of a single spin Alexander Wood, Lloyd C. L. Hollenberg, Robert E Scholten, Andy M Martin The theory of angular momentum connects physical rotations and quantum spins together at a fundamental level. Physical rotation of a quantum system will therefore affect fundamental quantum operations, such as spin rotations in projective Hilbert space, but these effects are subtle and experimentally challenging to observe due to the fragility of quantum coherence. Here we report a measurement of a single-electron-spin phase shift arising directly from physical rotation, without transduction through magnetic fields or ancillary spins. This phase shift is observed by measuring the difference between the phase of a microwave driving field and that of a rotating two-level electron spin system, a phase difference that can accumulate nonlinearly in time. We detect the nonlinear phase using spin-echo interferometry of a single nitrogen-vacancy qubit in a diamond rotating at 200,000 rpm. Our measurements demonstrate the fundamental connections between spin, physical rotation and quantum phase, and will be applicable in schemes where the rotational degree of freedom of a quantum system is not fixed, such as spin-based rotation sensors and trapped nanoparticles containing spins. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P07.00009: Long-living coherences and magnetic sensing with strongly-coupled quantum spins driven by pulse trains Viatcheslav Dobrovitski, Walter Hahn The systems comprised of a large number of strongly coupled quantum spins, driven by trains of 180° pulses, often demonstrate long-living quantum coherences, extending far beyond the "usual" coherence decay time (e.g. Hahn echo decay time) [1-3]. This effect is generic for various spin systems in different dimensions, from 1D to ∞-D (where every spin is coupled to all others), and the appearance of the long-living coherences is associated with the accumulated effect of the spin dynamics during the pulses (such as rotation angle deviating from 180°, or finite pulse width). |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P07.00010: Phase-estimation optimization in GaAs quantum dots Angel Gutierrez-Rubio, Peter Stano, Daniel Loss We address the optimization of phase estimation in the context of GaAs quantum dots [1]. This allows to track the hyperfine field in real time with maximum precision, quenching the main dephasing source. We prove that the mean entropy is the ultimate figure of merit to be minimized for such a purpose, in contrast to the ubiquitous use of the variance in the literature [2,3]. In accordance, non-adaptive and feedback strategies for the tunable interaction times are devised. Whereas global optimization is out of reach, we provide with the optimal offline strategy among the class of memoryless patterns. Remarkably, it indefinitely sustains its maximum precision despite frequency fluctuations and is robust in terms of self consistency. Moreover, we devise a computationally feasible online method to improve the precision for a given non-adaptive strategy, which could be applied to the experimental realization of Kitaev's algorithm. Finally, the scaling of the achieved precision beyond the shot-noise limit is discussed. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P07.00011: Imaging the crossover between ohmic and hydrodynamic electron flow in graphene with a single spin magnetometer Alec Jenkins, Susanne Baumann, Simon A Meynell, Haoxin Zhou, Daipeng Yang, Takashi Taniguchi, Kenji Watanabe, Andrew Lucas, Andrea Young, Ania Jayich In conventional conductors, transport is typically dominated by electron-phonon and electron-impurity scattering, giving rise to a direct proportionality between current and electric field known as Ohm’s law. In ultra-clean graphene devices where the momentum-conserving electron-electron interaction dominates, transport is expected to obey hydrodynamics in which the electrons behave like a classical fluid. By measuring the stray magnetic field created by the current flow, we directly image the crossover from ohmic to viscous flow in a high mobility graphene constriction using nitrogen-vacancy center magnetometry. At room temperature, current flow concentrates at the edges of the constriction regardless of carrier density, indicating ohmic transport. However, below 200K, we observe a crossover into the viscous flow where the current concentrates at the center of the constriction. Our imaging technique provides a direct observation of collision-dominated electron transport. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P07.00012: Sensing graphene density-of-states using a high-impedance resonator Charlotte Boettcher, Uri Vool, Joel Wang, Greg Calusine, David K Kim, Danna Rosenberg, Jonilyn Yoder, Amir Yacoby, William Oliver High-impedance superconducting resonators are important tools for quantum information and quantum sensing, as their resilience to magnetic fields and their highly concentrated local electric fields allow for strong coupling to small defects. |
Wednesday, March 4, 2020 4:54PM - 5:30PM |
P07.00013: Atomic-scale imaging of large nuclear-spin clusters using a quantum sensor Invited Speaker: Tim Hugo Taminiau Nuclear magnetic resonance (NMR) is a powerful method for determining the structure of molecules and proteins. While conventional NMR requires averaging over large ensembles, recent progress with single-spin quantum sensors has created the prospect of magnetic imaging of individual molecules and other spin systems. As an initial step towards this goal, isolated nuclear spins and spin pairs have been mapped. However, large clusters of interacting spins — such as found in molecules — result in highly complex spectra. Imaging these complex systems is an outstanding challenge due to the required high spectral resolution and efficient spatial reconstruction with sub-angstrom precision. Here we develop such atomic-scale imaging using a single nitrogen-vacancy (NV) centre as a quantum sensor, and demonstrate it on a model system of 27 coupled 13C nuclear spins in a diamond. We present a new multidimensional spectroscopy method that isolates individual nuclearnuclear spin interactions with high spectral resolution (< 80 mHz) and high accuracy (2 mHz). We show that these interactions encode the composition and inter-connectivity of the cluster, and develop methods to extract the 3D structure of the cluster with sub-angstrom resolution. These results demonstrate a key capability towards magnetic imaging of individual molecules and other complex spin systems. |
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