02007nas a2200181 4500008004100000245010800041210006900149260001500218520141700233100002201650700001901672700001901691700002001710700001901730700001701749700002201766856003701788 2023 eng d00aA general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors0 ageneral approach to backactionevading receivers with magnetomech c11/16/20233 a
Today's mechanical sensors are capable of detecting extremely weak perturbations while operating near the standard quantum limit. However, further improvements can be made in both sensitivity and bandwidth when we reduce the noise originating from the process of measurement itself -- the quantum-mechanical backaction of measurement -- and go below this 'standard' limit, possibly approaching the Heisenberg limit. One of the ways to eliminate this noise is by measuring a quantum nondemolition variable such as the momentum in a free-particle system. Here, we propose and characterize theoretical models for direct velocity measurement that utilize traditional electric and magnetic transducer designs to generate a signal while enabling this backaction evasion. We consider the general readout of this signal via electric or magnetic field sensing by creating toy models analogous to the standard optomechanical position-sensing problem, thereby facilitating the assessment of measurement-added noise. Using simple models that characterize a wide range of transducers, we find that the choice of readout scheme -- voltage or current -- for each mechanical detector configuration implies access to either the position or velocity of the mechanical sub-system. This in turn suggests a path forward for key fundamental physics experiments such as the direct detection of dark matter particles.
1 aRichman, Brittany1 aGhosh, Sohitri1 aCarney, Daniel1 aHiggins, Gerard1 aShawhan, Peter1 aLobb, C., J.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2311.0958701777nas a2200241 4500008004100000245007500041210006900116260001400185490000700199520107300206100001801279700002701297700001801324700001901342700001701361700002101378700001901399700002101418700002001439700001701459700002201476856003701498 2008 eng d00aMultilevel effects in the Rabi oscillations of a Josephson phase qubit0 aMultilevel effects in the Rabi oscillations of a Josephson phase c2008/9/150 v783 a We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states. 1 aDutta, S., K.1 aStrauch, Frederick, W.1 aLewis, R., M.1 aMitra, Kaushik1 aPaik, Hanhee1 aPalomaki, T., A.1 aTiesinga, Eite1 aAnderson, J., R.1 aDragt, Alex, J.1 aLobb, C., J.1 aWellstood, F., C. uhttp://arxiv.org/abs/0806.4711v201333nas a2200181 4500008004100000245004900041210004900090260001400139490000700153520083600160100001900996700002001015700001701035700002101052700002201073700001901095856003701114 2008 eng d00aQuantum behavior of the dc SQUID phase qubit0 aQuantum behavior of the dc SQUID phase qubit c2008/6/130 v773 a We analyze the behavior of a dc Superconducting Quantum Interference Device (SQUID) phase qubit in which one junction acts as a phase qubit and the rest of the device provides isolation from dissipation and noise in the bias leads. Ignoring dissipation, we find the two-dimensional Hamiltonian of the system and use numerical methods and a cubic approximation to solve Schrodinger's equation for the eigenstates, energy levels, tunneling rates, and expectation value of the currents in the junctions. Using these results, we investigate how well this design provides isolation while preserving the characteristics of a phase qubit. In addition, we show that the expectation value of current flowing through the isolation junction depends on the state of the qubit and can be used for non-destructive read out of the qubit state. 1 aMitra, Kaushik1 aStrauch, F., W.1 aLobb, C., J.1 aAnderson, J., R.1 aWellstood, F., C.1 aTiesinga, Eite uhttp://arxiv.org/abs/0805.3680v1