Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y17: Focus Session: Quantum Metrology and Nanomechanics |
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Sponsoring Units: GQI Chair: David DiVincenzo, IBM Room: 318 |
Friday, March 20, 2009 8:00AM - 8:36AM |
Y17.00001: High-sensitivity diamond magnetometer with nanoscale resolution Invited Speaker: We will discuss our recent work on using isolated electronic spins in the solid-state as sensitive magnetic sensors [1,2]. This novel approach to magnetometry is enabled by the good coherence properties of electronic qubits, such as the spins associated with Nitrogen-Vacancy (NV) centers in diamond, as well as by advanced techniques for their coherent control. The key feature of this solid-state magnetometer is the possibility to confine the sensing spins into a crystal of nanometer size that can be brought extremely close to the magnetic field source, thus achieving high spatial resolution. Our first experiments demonstrate that the resulting magnetic sensor provides an unprecedented combination of ultra-high sensitivity and spatial resolution. The ultimate sensitivity limit is set by the interaction of the spin sensor with its environment and in particular the nuclear and electronic spin bath. As an outlook, we will discuss how engineering, controlling or harnessing the environment can lead to better sensitivity, even beyond the standard quantum limit. Finally, we will outline several exciting applications of the novel magnetic sensors in areas ranging from bio- and materials science to fundamental physics and single electronic and nuclear spin detection. \\[4pt] [1] J. M. Taylor, et al. Nature Phys. 4, 810-816 (2008). \\[0pt] [2] J. R. Maze, et al. Nature 455, 644 - 647 (2008) [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y17.00002: Coupling Nitrogen Vacancy Centers in a Diamond Nanopillar to a Silica Microsphere Khodadad Dinyari, Mats Larsson, Hailin Wang Nitrogen vacancy (NV) centers in a diamond nanopillar have been coupled to the whispering gallery modes (WGMs) of a silica microsphere. The NV centers were coupled to the WGMs by positioning a nanopillar near the equator of the microsphere with nanometer precision. For cavity QED studies, WGMs with $l=m$ are of interest due to their small mode volumes. It was observed that when a 200 nm diameter nanopillar was optimally coupled to this particular mode in a 50 $\mu m$ diameter microsphere, the quality factor (Q) was only reduced to 2x10$^{6}$ from an initial Q of 6x10$^{6}$. The nanopillars were fabricated from a bulk single crystal diamond by means of reactive ion etching, resulting in nanopillars with diameters as small as 200 nm with a height of approximately 1 $\mu m$. We estimate that a 140 nm pillar would allow a cavity linewidth of order 20 MHz, comparable to the zero phonon linewidth of a NV center. Producing a nanopillar with a 140 nm diameter is well within our fabrication technique making this composite system a suitable candidate for strong-coupling cavity QED. This nanopillar-microsphere system circumvents the poor controllability of nanocrystal based microresonator systems and utilizes the exceptional properties of both NV centers in bulk crystals and the ultra-high Q of silica microspheres. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y17.00003: An Ensemble of NV-centers in Diamond Coupled to a Flux Qubit David Marcos, Martijn Wubs, R. Aguado, M.D. Lukin, Anders Sorensen In the last years, the interface between quantum optics and solid state physics has been explored, and various models for hybrid qubits have been proposed. We consider a superconducting flux qubit coupled to an ensemble of NV-centers in diamond. An effective model is derived, showing how coherent transfer between both two level systems can be achieved, and the possible advantages of the system as the building block of a quantum computer. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y17.00004: Getting Information on Independently Prepared Quantum States -- When are Individual Measurements as Powerful as Joint Measurements? Chi-Hang Fred Fung, H. F. Chau Given a composite quantum system in which the states of the subsystems are independently (but not necessarily identically) prepared, we construct separate measurements on the subsystems from any given joint measurement such that the former always give at least as large information as the latter. This construction offers new insights into the understanding of measurements on this type of composite systems. Moreover, this construction essentially proves the intuition that separate measurements on the subsystems are sufficient to extract the maximal information about the separately prepared subsystems, thus making a joint measurement unnecessary. Furthermore, our result implies that individual attacks are as powerful as collective attacks in obtaining information on the raw key in quantum key distribution. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y17.00005: Quantum noise interference as a route to ground state cooling in cavity electromechanics Aashish Clerk, Florian Elste, Steve Girvin We present a theoretical analysis of a novel cavity electromechanical (or optomechanical) system where a mechanical resonator directly modulates the damping rate $\kappa$ of a driven microwave (or optical) cavity. We show that due to a destructive interference of quantum noise, the driven cavity can effectively act like a zero-temperature bath {\it irrespective} of the ratio $\kappa / \omega_M$, where $\omega_M$ is the mechanical frequency. This scheme thus allows one to cool the mechanical resonator to its ground state without requiring the cavity to be in the so-called good cavity limit $\kappa \ll \omega_M$. This behavior is in sharp contrast to the more common setup with a parametric coupling (where the mechanics modulates the frequency of the cavity); there, ground state cooling is only possible in the good cavity limit [1,2]. We also show that this system can be used to perform quantum-limited position measurements. The system described here could be implemented directly using setups similar to those used in recent experiments in cavity electromechanics [3]. \\[4pt] [1]~F. Marquardt \textit{et al.}, Phys.\ Rev.Lett.\ \textbf{99}, 093902 (2007).\\[0pt] [2]~I. Wilson-Rae \textit{et al.}, Phys.Rev.\ Lett.\ \textbf{99}, 093901 (2007).\\[0pt] [3]~J. D. Teufel \textit{et al.}, Phys.\ Rev.Lett.\ \textbf{101}, 197203 (2008). [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y17.00006: Force sensitivity of a nanomechanical oscillator in a microwave cavity Jennifer Harlow, John Teufel, Tobias Donner, Konrad Lehnert We describe our efforts to realize ultrasensitive force detection based on sensing the motion of nanomechanical oscillators embedded in superconducting resonant microwave cavities. Such a force sensor requires a readout mechanism quiet enough that the sensitivity is limited by thermal noise of the oscillator, as we recently demonstrated [1]. Force sensitivity is optimized by low mass, high-Q mechanical oscillators which have been cooled to dilution refrigeration temperatures. With this goal in mind, we fabricate high-Q ($Q>10^5$), picogram mechanical beams with MHz resonance frequencies. We report measurements with sub-$aN/\sqrt{Hz}$ force sensitivity and discuss prospects for further progress. [1] C. A. Regal, J. D. Teufel, and K. W. Lehnert, Nature Physics 4, 555 (2008). [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y17.00007: Resolved-Sideband Cooling of Nanomechanical Motion within a Microwave Cavity John Teufel, Jennifer Harlow, Tobias Donner, Michael Demoret, Konrad Lehnert We present recent experiments in which we couple the motion of a high-Q nanomechanical oscillator to the microwave fields in a superconducting resonant circuit [1]. This microwave optomechanical system is operated in the resolved-sideband regime in which the mechanical resonance frequency exceeds the cavity bandwidth. In this regime, the dynamical backaction of the microwave radiation further cools the mechanical motion from dilution refrigerator temperatures to even lower thermal occupancy. Recent improvements increase both the optomechanical coupling strength and the power handling capability of the cavity. We report progress toward cooling to the mechanical ground state with this system. [1] J. D. Teufel, J. W. Harlow, C. A. Regal and K. W. Lehnert, Phys. Rev. Lett., 101, 197203 (2008). [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y17.00008: Photon-Mediated Magnetic Cooling of~a Micromechanical Oscillator Joonho Jang, Raffi Budakian In recent years, a number of techniques have been developed to cool a mode of a micromechanical oscillator to the ground state. In this talk, I will present a new scheme for cooling a micromechanical oscillator involving the interaction of a micron-size superconductor, attached to the cantilever, with an external magnetic field. When the cantilever is placed inside an optical cavity, the absorption of photons by the superconductor gives rise to a retarded force that modifies the damping of the oscillator. Initial measurements using NbSe$_{2}$, show approximately a factor of 25 reduction in the mode temperature from 5 K to 200 mK. By optimizing the cavity finesse, the magnetic field configuration, and the superconductor quasiparticle lifetime, a further reduction of 10$^{3}${\-}10$^{4}$ in the cantilever mode temperature could be realized. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y17.00009: Parametric Amplification and Detection of Nanomechanical Motion Jared Hertzberg, Tristan Rocheleau, Tchefor Ndukum, Keith Schwab We have performed experiments with a 5.57 MHz nanomechanical resonator (NR) capacitively coupled to a 5 GHz superconducting microwave resonator and cooled to a temperature of 142mK. When driving with two microwave tones, a configuration appropriate for back-action evading measurements of a single motional quadrature, we find that a parametric instability appears at high drive powers. Due to the interference of the microwave tones, the capacitive frequency shift of the NR is periodically modulated at twice the mechanical frequency, resulting in a degenerate parametric amplification of the mechanical motion. In this regime, we demonstrate mechanical gains of up to 11.6dB and parametrically reduced linewidths of 2.1 Hz, resulting in a position resolution near the standard quantum limit. Although this effect is expected to limit the back-action evasion dynamics, it is useful for mechanical preamplification and noise squeezing, subjects of future work. [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y17.00010: Back action evading quantum limited measurements of a nanomechanical resonator Tchefor Ndukum, Tristan Rocheleau, Jared Hertzberg, Keith Schwab By driving a 5GHz superconducting, co-planar waveguide (CPW) resonator coupled to a radio-frequency nanomechanical resonator with both red- and blue-detuned, phase coherent microwave signals, we demonstrate amplifier noise back action evading(BAE) detection of one quadrature of nanomechanical motion. With this method we show precise measurements of a single motional quadrature with additive measurement noise of 4 times the zero point amplitude, and a reduction in sensitivity to injected measurement noise of a factor of 43 in comparison to a single tone, non-BAE measurement. We have also found a parametric instability which limits the coupling strength possible in our device, which will be described elsewhere. With straightforward improvements to the microwave resonator, we expect to be able to demonstrate sensitivity to one quadrature with additive measurement noise below the zero-point level, a necessary ingredient to produce and measure squeezed states of motion. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y17.00011: Sideband Resolved Cooling of a Nanomechanical Resonator Parametrically Coupled to a Microwave Resonator Tristan Rocheleau, Tchefor Ndukum, Jared Hertzberg, Keith Schwab We have fabricated a nanostructure formed by a radio-frequency nanomechanical (NEMS) resonator capacitively coupled to an aluminum 5 GHz superconducting, co-planar waveguide (CPW) resonator with 50 $\Omega$ characteristic impedance.By driving this coupled system at a frequency $\omega_{pump} =\omega_{CPW} - \omega_{NEMS}$, we demonstrate back action cooling effects of a single NEMS mode achieving cooling from temperatures of 100mK to $<$10mK, with the lowest occupation factor of N$<$30. We have recently demonstrated a Nb, 130 $\Omega$ 5 GHz, Q=15,000 microwave resonator which we expect to be capable of cooling the NEMS close to ground state. [Preview Abstract] |
Friday, March 20, 2009 10:36AM - 10:48AM |
Y17.00012: Ground state cooling of nanomechanical resonator via linear coupling in a superconducting circuit Lin Tian In recent experiments, it has been demonstrated that radiation pressure-like coupling between a nanomechanical resonator and a superconducting resonator can be explored for the cooling of the nanomechanical mode. In this work, We present a ground state cooling scheme for a nanomechanical resonator linearly coupled with a superconducting LC oscillator. The linear coupling, when periodically modulated at red detuning, up-converts the low-frequency nanomechanical mode to the high- frequency LC oscillator mode and generates backaction force that can cool the nanomechanical mode to its ground state in the resolved-sideband regime. Compared with schemes using radiation pressure-like coupling, the LC oscillator mode doesn't need to be driven to high photon occupation number in our scheme. We calculate the cooling rate and the stationary occupation number of the nanomechanical mode and show that ground state can be reached with practical device parameters. A detailed study of our model shows that the quantum backaction noise that limits the cooling process is due to the counter rotating terms in the linear coupling. The scheme can be compared with laser cooling for the atomic systems as well. [Preview Abstract] |
Friday, March 20, 2009 10:48AM - 11:00AM |
Y17.00013: Quantum Measurements of Coupled Systems L. Fedichkin, M. Shapiro, M. I. Dykman Quantum measurements are often performed on coupled systems. Such measurements are of interest for various proposed realizations of a quantum computer where the qubit-qubit coupling may not be completely turned off. Because of the coupling, the stationary state wave functions are not fully localized on individual qubits even where the energies of neighboring qubits are tuned away from each other. As a result, an instantaneous projective single-qubit measurement gives the state population with an error. We show that the error may be significantly reduced. This is accomplished by tuning the detector close to resonance with the measured qubit. The qubit- detector coupling should be small compared to the decay width $\gamma$ of the excited level of the detector. For such tuning, there is a broad time interval where the probability of an error in detecting an excitation on the resonant qubit and distinguishing it from other excitations is smaller than that for a projective measurement by a factor $\sim (\gamma/\Delta E)^2$, where $\Delta E$ is the difference in the qubit energies. The results bear on the scalability of quantum computers with permanently coupled qubits. [Preview Abstract] |
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