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Author |
Grinolds, M. S.; Maletinsky, P.; Hong, S.; Lukin, M. D.; Walsworth, R. L.; Yacoby, A. |
Title |
Quantum control of proximal spins using nanoscale magnetic resonance imaging |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
9 |
Pages |
687-692 |
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fromIPMRAS |
Abstract |
Quantum control of individual spins in condensed-matter systems is an emerging field with wide-ranging applications in spintronics, quantum computation and sensitive magnetometry. Recent experiments have demonstrated the ability to address and manipulate single electron spins through either optical or electrical techniques. However, it is a challenge to extend individual-spin control to nanometre-scale multi-electron systems, as individual spins are often irresolvable with existing methods. Here we demonstrate that coherent individual-spin control can be achieved with few- nanometre resolution for proximal electron spins by carrying out single-spin magnetic resonance imaging (MRI), which is realized using a scanning-magnetic-field gradient that is both strong enough to achieve nanometre spatial resolution and sufficiently stable for coherent spin manipulations. We apply this scanning-field-gradient MRI technique to electronic spins in nitrogen-vacancy (NV) centres in diamond and achieve nanometre resolution in imaging, characterization and manipulation of individual spins. For NV centres, our results in individual-spin control demonstrate an improvement of nearly two orders of magnitude in spatial resolution when compared with conventional optical diffraction-limited techniques. This scanning-field-gradient microscope enables a wide range of applications including materials characterization, spin entanglement and nanoscale magnetometry. |
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RPLAB @ gujma @ |
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827 |
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Dada, Adetunmise C.; Leach, Jonathan; Buller, Gerald S.; Padgett, Miles J.; Andersson, Erika |
Title |
Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
9 |
Pages |
677-680 |
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fromIPMRAS |
Abstract |
Quantum entanglement plays a vital role in many quantum-information and communication tasks. Entangled states of higher-dimensional systems are of great interest owing to the extended possibilities they provide. For example, they enable the realization of new types of quantum information scheme that can offer higher-information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems (see ref. and references therein). Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher-dimensional entangled systems are used. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalized to d-dimensional systems up to d=12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum, generated through spontaneous parametric down-conversion, and manipulated using computer-controlled holograms. |
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RPLAB @ gujma @ |
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828 |
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Bylander, Jonas; Gustavsson, Simon; Yan, Fei; Yoshihara, Fumiki; Harrabi, Khalil; Fitch, George; Cory, David G.; Nakamura, Yasunobu; Tsai, Jaw-Shen; Oliver, William D. |
Title |
Noise spectroscopy through dynamical decoupling with a superconducting flux qubit |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
7 |
Pages |
565-570 |
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fromIPMRAS |
Abstract |
Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1=12μs. We first demonstrate that dynamical decoupling improves the coherence time T2 in this system up to the T2=2T1 limit (pure dephasing times exceeding 100μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20MHz, observing a 1/fα distribution with α<1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence. |
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RPLAB @ gujma @ |
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829 |
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Author |
Baumert, Thomas |
Title |
Quantum technology: Wave packets get a kick |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
5 |
Pages |
373-374 |
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fromIPMRAS |
Abstract |
Intense femtosecond pulses of infrared light can manipulate molecules. It is now shown that such control even extends to making different molecular eigenstates interfere with each other in a way never considered before -- a potential tool for optically engineered chemical reactions and for ultrafast information encoding and manipulation. |
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RPLAB @ gujma @ |
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830 |
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Bozyigit, D.; Lang, C.; Steffen, L.; Fink, J. M.; Eichler, C.; Baur, M.; Bianchetti, R.; Leek, P. J.; Filipp, S.; da Silva, M. P.; Blais, A.; Wallraff, A. |
Title |
Antibunching of microwave-frequency photons observed in correlation measurements using linear detectors |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
2 |
Pages |
154-158 |
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fromIPMRAS |
Abstract |
At optical frequencies the radiation produced by a source, such as a laser, a black body or a single-photon emitter, is frequently characterized by analysing the temporal correlations of emitted photons using single-photon counters. At microwave frequencies, however, there are no efficient single-photon counters yet. Instead, well-developed linear amplifiers allow for efficient measurement of the amplitude of an electromagnetic field. Here, we demonstrate first- and second-order correlation function measurements of a pulsed microwave-frequency single-photon source integrated on the same chip with a 50/50 beam splitter followed by linear amplifiers and quadrature amplitude detectors. We clearly observe single-photon coherence in first-order and photon antibunching in second-order correlation function measurements of the propagating fields. |
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RPLAB @ gujma @ |
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835 |
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Author |
Kumar, Sushil; Wang I. Chan, Chun; Hu, Qing; Reno, John L. |
Title |
A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
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Pages |
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fromIPMRAS |
Abstract |
Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~ω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9ω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser. |
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RPLAB @ gujma @ |
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836 |
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Mariantoni, Matteo; Wang, H.; Bialczak, Radoslaw C.; Lenander, M.; Lucero, Erik; Neeley, M.; O'Connell, A. D.; Sank, D.; Weides, M.; Wenner, J.; Yamamoto, T.; Yin, Y.; Zhao, J.; Martinis, John M.; Cleland, A. N. |
Title |
Photon shell game in three-resonator circuit quantum electrodynamics |
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Journal Article |
Year |
2011 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
4 |
Pages |
287-293 |
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fromIPMRAS |
Abstract |
The generation and control of quantum states of light constitute fundamental tasks in cavity quantum electrodynamics (QED). The superconducting realization of cavity QED, circuit QED (refs 11, 12, 13, 14), enables on-chip microwave photonics, where superconducting qubits control and measure individual photon states. A long-standing issue in cavity QED is the coherent transfer of photons between two or more resonators. Here, we use circuit QED to implement a three-resonator architecture on a single chip, where the resonators are interconnected by two superconducting phase qubits. We use this circuit to shuffle one- and two-photon Fock states between the three resonators, and demonstrate qubit-mediated vacuum Rabi swaps between two resonators. By shuffling superposition states we are also able to demonstrate the high-fidelity phase coherence of the transfer. Our results illustrate the potential for using multi-resonator circuits as photon quantum registers and for creating multipartite entanglement between delocalized bosonic modes. |
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RPLAB @ gujma @ |
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838 |
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Buchanan, Mark |
Title |
Nothing's impossible |
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Manuscript |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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5 |
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fromIPMRAS |
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RPLAB @ gujma @ |
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839 |
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Author |
Lupascu, Adrian |
Title |
Nonlinear dynamics: Quantum pendula locked in |
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Journal Article |
Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
Volume |
7 |
Issue |
2 |
Pages |
100-101 |
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fromIPMRAS |
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A study of the autoresonant behaviour of a superconducting pendulum reveals that quantum fluctuations determine only the initial oscillator motion and not its subsequent dynamics. This could be important in the development of more efficient methods for reading solid-state qubits. |
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RPLAB @ gujma @ |
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840 |
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Nevou, L.; Liverini, V.; Friedli, P.; Castellano, F.; Bismuto, A.; Sigg, H.; Gramm, F.; Müller, E.; Faist, J. |
Title |
Current quantization in an optically driven electron pump based on self-assembled quantum dots |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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423–427 |
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fromIPMRAS |
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The electronic structure of self-assembled semiconductor quantum dots consists of discrete atom-like states that can be populated with a well-defined number of electrons. This property can be used to fabricate a d.c. current standard that enables the unit of ampere to be independently defined. Here we report an optically pumped current source based on self-assembled InAs/GaAs quantum dots. The accuracy obtained so far is 10–1 and is limited by the uncertainty in the number of dots. At 10 K the device generates a current difference of 2.39 nA at a frequency of 1 kHz. The accuracy could be improved by site-selective growth techniques where the number of dots is fixed by pre-patterning. The results are promising for applications in electrical metrology, where a current standard is needed to close the so-called quantum metrological triangle. |
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RPLAB @ gujma @ |
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841 |
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Ma, Xiao-Song; Dakic, Borivoje; Naylor, William; Zeilinger, Anton; Walther, Philip |
Title |
Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
Volume |
7 |
Issue |
5 |
Pages |
399-405 |
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fromIPMRAS |
Abstract |
Quantum simulators are controllable quantum systems that can reproduce the dynamics of the system of interest in situations that are not amenable to classical computers. Recent developments in quantum technology enable the precise control of individual quantum particles as required for studying complex quantum systems. In particular, quantum simulators capable of simulating frustrated Heisenberg spin systems provide platforms for understanding exotic matter such as high-temperature superconductors. Here we report the analogue quantum simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type interactions among four spin-1/2 particles. Depending on the interaction strength, frustration within the system emerges such that the ground state evolves from a localized to a resonating-valence-bond state. This spin-1/2 tetramer is created using the polarization states of four photons. The single-particle addressability and tunable measurement-induced interactions provide us with insights into entanglement dynamics among individual particles. We directly extract ground-state energies and pairwise quantum correlations to observe the monogamy of entanglement. |
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RPLAB @ gujma @ |
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842 |
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Mineev, Vladimir P. |
Title |
Superfluid helium: Order in disorder |
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Journal Article |
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2012 |
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Nature Physics |
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Nat. Phys. |
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8 |
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253–254 |
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fromIPMRAS |
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Confining liquid 3He in porous silica aerogel prepared with strong anisotropy stabilizes a state of axial superfluidity. |
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RPLAB @ gujma @ |
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810 |
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Clerk, Aashish |
Title |
Quantum phononics: To see a SAW |
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Journal Article |
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2012 |
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Nature Physics |
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Nat. Phys. |
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8 |
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4 |
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256-257 |
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fromIPMRAS |
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Mechanical oscillations of microscopic resonators have recently been observed in the quantum regime. This idea could soon be extended from localized vibrations to travelling waves thanks to a sensitive probe of so-called surface acoustic waves. |
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RPLAB @ gujma @ |
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811 |
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Hollenberg, Lloyd C. L. |
Title |
Quantum control: Through the quantum chicane |
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Journal Article |
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2012 |
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Nature Physics |
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Nat. Phys. |
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8 |
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2 |
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113-114 |
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In quantum control there is an inherent tension between high fidelity requirements and the need for speed to avoid decoherence. A direct comparison of quantum control protocols at these two extremes indicates where the sweet spot may lie. |
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812 |
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Gustafsson, Martin V.; Santos, Paulo V.; Johansson, Göran; Delsing, Per |
Title |
Local probing of propagating acoustic waves in a gigahertz echo chamber |
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2012 |
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Nature Physics |
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Nat. Phys. |
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8 |
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4 |
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338-343 |
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In the same way that micro-mechanical resonators resemble guitar strings and drums, surface acoustic waves resemble the sound these instruments produce, but moving over a solid surface rather than through air. In contrast with oscillations in suspended resonators, such propagating mechanical waves have not before been studied near the quantum mechanical limits. Here, we demonstrate local probing of surface acoustic waves with a displacement sensitivity of 30amRMSHz-1/2 and detection sensitivity on the single-phonon level after averaging, at a frequency of 932MHz. Our probe is a piezoelectrically coupled single-electron transistor, which is sufficiently fast, non-destructive and localized to enable us to track pulses echoing back and forth in a long acoustic cavity, self-interfering and ringing the cavity up and down. We project that strong coupling to quantum circuits will enable new experiments, and hybrids using the unique features of surface acoustic waves. Prospects include quantum investigations of phonon-phonon interactions, and acoustic coupling to superconducting qubits for which we present favourable estimates. |
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RPLAB @ gujma @ |
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813 |
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