



@article {3408,
	title = {A general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors},
	year = {2023},
	month = {11/16/2023},
	abstract = {<p>Today\&$\#$39;s mechanical sensors are capable of detecting extremely weak perturbations while operating near the standard quantum limit. However, further improvements can be made in both sensitivity and bandwidth when we reduce the noise originating from the process of measurement itself -- the quantum-mechanical backaction of measurement -- and go below this \&$\#$39;standard\&$\#$39; 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.</p>},
	url = {https://arxiv.org/abs/2311.09587},
	author = {Brittany Richman and Sohitri Ghosh and Daniel Carney and Gerard Higgins and Peter Shawhan and C. J. Lobb and Jacob M. Taylor}
}
@article {1305,
	title = {Multilevel effects in the Rabi oscillations of a Josephson phase qubit},
	journal = {Physical Review B},
	volume = {78},
	year = {2008},
	month = {2008/9/15},
	abstract = {  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.
},
	doi = {10.1103/PhysRevB.78.104510},
	url = {http://arxiv.org/abs/0806.4711v2},
	author = {S. K. Dutta and Frederick W. Strauch and R. M. Lewis and Kaushik Mitra and Hanhee Paik and T. A. Palomaki and Eite Tiesinga and J. R. Anderson and Alex J. Dragt and C. J. Lobb and F. C. Wellstood}
}
@article {1300,
	title = {Quantum behavior of the dc SQUID phase qubit},
	journal = {Physical Review B},
	volume = {77},
	year = {2008},
	month = {2008/6/13},
	abstract = {  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{\textquoteright}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.
},
	doi = {10.1103/PhysRevB.77.214512},
	url = {http://arxiv.org/abs/0805.3680v1},
	author = {Kaushik Mitra and F. W. Strauch and C. J. Lobb and J. R. Anderson and F. C. Wellstood and Eite Tiesinga}
}
