This year’s APS March Meeting in Baltimore was unquestionably a good one. It seemed like everyone showed up. We were happy to be able to give an invited talk on cavity quantum phonodynamics and two theory talks on our work on quantum dot spin-valley relaxation with the Australians and on the theory of proposed many-body phononic systems. Also of note were the two sessions on Quantum Characterization, Verification, and Validation (I, II) and the four(!) on nano/optomechanics (I, II, III, IV).
Abstract: N27.00001 : On-chip cavity quantum phonodynamics: spin qubits and nano/optomechanics (Invited)
Author: Charles Tahan (Laboratory for Physical Sciences)
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Sound can be just as quantum as light. But our toolbox for single quanta of sound, i.e. phonons, is currently insufficient. Here we propose a new component that enables a chip-based, solid-state analogue of cavity-QED utilizing acoustic phonons instead of photons. We show how long-lived and tunable acceptor impurity states in silicon nanomechanical cavities can play the role of a matter non-linearity for coherent phonons just as, for example, the Josephson qubit plays in circuit-QED. Both strong coupling (number of coherent Rabi oscillations of approximately 100) and strong dispersive coupling (0.1-2 MHz) can be reached in the 1-20 GHz frequency range, making the system compatible with existing high-Q, nanomechanical resonators. We give explicit experimental signatures and measurement protocols of the acceptor-cavity system via a phonon probe. This system enables the control of single phonons and phonon-phonon interactions, dispersive phonon readout of the acceptor qubit, and compatibility with other nano/optomechanical components such as phonon-photon translators. (This work in collaboration with Rusko Ruskov, LPS; work with Oney Soykal, LPS, will also be discussed.)
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Authors: Rusko Ruskov, Charles Tahan (Laboratory for Physical Sciences)
We consider spin and valley relaxation in imperfect silicon quantum dots with 1 to 3 electrons. Phonons, spin-orbit coupling, and the electrostatic confining potential of the dot all play roles in both the functional dependence on key parameters (say magnetic field) and the quantitative magnitude of the relaxation rate. Level mixing in the dot allows for spin relaxation via phonons and also explains anti-crossing behavior of dot levels as a function of magnetic field. We show that valley state relaxation can be fast in realistic dots and that spin relaxation can be a few orders of magnitude longer. Our results compare favorably to recent experimental data including the power dependence on magnetic field, location of relaxation hot spots, and the magnitude of the relaxation rates themselves. Some of this work is in collaboration with A. Dzurak group at the University of New South Wales, Australia.
Xiaojie Hao, Ming Xiao, Hongwen Jiang (Department of Physics and Astronomy, University of California at Los Angeles)
Rusko Ruskov Charles Tahan (Laboratory for Physical Sciences, USA)
Pauli spin blockade is used as a means to detect the flip of spins in a silicon metal-oxide-semiconductor (MOS) based double quantum dot. Microwave driven electron spin resonance (ESR) signals, with a linewidth as narrow as 1.5 G, has been observed only in a narrow range of magnetic fields. ESR spectroscopy in the magnetic field – microwave frequency plane shows an unexpected level anti-crossing, with an energy gap of about 50 MHz. The spectral line gives an estimation of the lower bound for inhomogeneous phase decoherence time T∗2 of about a couple of hundred ns for individual spins in the nano-structured system with a Si/SiO2 interface. We explain the anti-crossing gap as due to spin-orbit mixing with higher states, which is also responsible for the narrow-window visibility of the ESR signal in Si based double quantum dots.
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(University of Maryland)
(Laboratory for Physical Sciences)
We previously proposed a nano-mechanical system where phonons trapped in an acoustic cavity can strongly hybridize with impurity qubit states in silicon (forming a so-called cavity-phoniton). Here, we extend the idea to the quantum many-body limit by investigating the physics of phonon-tunnel-coupled arrays of such components. The silicon qubit cavity phoniton system potentially offers advantages in this regime over purely optomechanical systems where the optomechanical coupling is still quite small. First, single phonons in a crystal can have large effective de Broglie wavelengths (microns). Second, as we have previously shown, qubit-phonon coupling can be quite large, easily allowing the system to enter the strong coupling regime and enabling phonon-blockade. Such arrays can be fabricated in semiconductor heterostructures or in on-chip, optomechanical crystals. We calculate the parameter regime where the Mott-Superfluid quantum phase transition occurs in realizable devices. We also demonstrate the emergence of super-splitting, phonon anti-bunching, and phonon blockade through the non-equilibrium density matrix master equation approach in few cavity systems.