No Arabic abstract
We analyze the dynamics of a nano-mechanical resonator coupled to a single-electron transistor (SET) in the regime where the resonator behaves classically. A master equation is derived describing the dynamics of the coupled system which is then used to obtain equations of motion for the average charge state of the SET and the average position of the resonator. We show that the action of the SET on the resonator is very similar to that of a thermal bath, as it leads to a steady-state probability-distribution for the resonator which can be described by mean values of the resonator position, a renormalized frequency, an effective temperature and an intrinsic damping constant. Including the effects of extrinsic damping and finite temperature, we find that there remain experimentally accessible regimes where the intrinsic damping of the resonator still dominates its behavior. We also obtain the average current through the SET as a function of the coupling to the resonator.
We present an analysis of the dynamics of a nanomechanical resonator coupled to a superconducting single electron transistor (SSET) in the vicinity of the Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP) resonances. For weak coupling and wide separation of dynamical timescales, we find that for either superconducting resonance the dynamics of the resonator is given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an equilibrium heat bath, characterised by an effective temperature, which also damps the resonator and renormalizes its frequency. Depending on the gate and drain-source voltage bias points with respect to the superconducting resonance, the SSET can also give rise to an instability in the mechanical resonator marked by negative damping and temperature within the appropriate Fokker-Planck equation. Furthermore, sufficiently close to a resonance, we find that the Fokker-Planck description breaks down. We also point out that there is a close analogy between coupling a nanomechanical resonator to a SSET in the vicinity of the JQP resonance and Doppler cooling of atoms by means of lasers.
We have suspended an Al based single-electron transistor whose island can resonate freely between the source and drain leads forming the clamps. In addition to the regular side gate, a bottom gate with a larger capacitance to the SET island is placed underneath to increase the SET coupling to mechanical motion. The device can be considered as a doubly clamped Al beam that can transduce mechanical vibrations into variations of the SET current. Our simulations based on the orthodox model, with the SET parameters estimated from the experiment, reproduce the observed transport characteristics in detail.
The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen-vacancy center spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen-vacancy spin-strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen-vacancy center. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen-vacancy ground state spin. The nitrogen-vacancy center is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 10^(-6) strain Hz^(-1/2). Finally, we show how this spin-resonator system could enable coherent spin-phonon interactions in the quantum regime.
We report on combined measurements of heat and charge transport through a single-electron transistor. The device acts as a heat switch actuated by the voltage applied on the gate. The Wiedemann-Franz law for the ratio of heat and charge conductances is found to be systematically violated away from the charge degeneracy points. The observed deviation agrees well with the theoretical expectation. With large temperature drop between the source and drain, the heat current away from degeneracy deviates from the standard quadratic dependence in the two temperatures.
We present a linear-response theory for the thermopower of a single-electron transistor consisting of a superconducting island weakly coupled to two normal-conducting leads (NSN SET). The thermopower shows oscillations with the same periodicity as the conductance and is rather sensitive to the size of the superconducting gap. In particular, the previously studied sawtooth-like shape of the thermopower for a normal-conducting single-electron device is qualitatively changed even for small gap energies.