11 research outputs found
Time-Domain Terahertz Spectroscopy in High Magnetic Fields
There are a variety of elementary and collective terahertz-frequency
excitations in condensed matter whose magnetic field dependence contains
significant insight into the states and dynamics of the electrons involved.
Often, determining the frequency, temperature, and magnetic field dependence of
the optical conductivity tensor, especially in high magnetic fields, can
clarify the microscopic physics behind complex many-body behaviors of solids.
While there are advanced terahertz spectroscopy techniques as well as high
magnetic field generation techniques available, combination of the two has only
been realized relatively recently. Here, we review the current state of
terahertz time-domain spectroscopy experiments in high magnetic fields. We
start with an overview of time-domain terahertz detection schemes with a
special focus on how they have been incorporated into optically accessible
high-field magnets. Advantages and disadvantages of different types of magnets
in performing terahertz time-domain spectroscopy experiments are also
discussed. Finally, we highlight some of the new fascinating physical phenomena
that have been revealed by terahertz time-domain spectroscopy in high magnetic
fields
Flexible Integration of Gigahertz Nanomechanical Resonators with a Superconducting Microwave Resonator using a Bonded Flip-Chip Method
We demonstrate strong coupling of gigahertz-frequency nanomechanical
resonators to a frequency-tunable superconducting microwave resonator via a
galvanically bonded flip-chip method. By tuning the microwave resonator with an
external magnetic field, we observe a series of hybridized microwave-mechanical
modes and report coupling strengths of at cryogenic
temperatures. The demonstrated multi-chip approach provides flexible rapid
characterization and simplified fabrication, and could potentially enable
coupling between a variety of quantum systems. Our work represents a step
towards a plug-and-play architecture for building more complex hybrid quantum
systems.Comment: 10 pages, 8 figures. First three authors contributed equally to this
wor
Analysis of arbitrary superconducting quantum circuits accompanied by a Python package: SQcircuit
Superconducting quantum circuits are a promising hardware platform for
realizing a fault-tolerant quantum computer. Accelerating progress in this
field of research demands general approaches and computational tools to analyze
and design more complex superconducting circuits. We develop a framework to
systematically construct a superconducting quantum circuit's quantized
Hamiltonian from its physical description. As is often the case with quantum
descriptions of multicoordinate systems, the complexity rises rapidly with the
number of variables. Therefore, we introduce a set of coordinate
transformations with which we can find bases to diagonalize the Hamiltonian
efficiently. Furthermore, we broaden our framework's scope to calculate the
circuit's key properties required for optimizing and discovering novel qubits.
We implement the methods described in this work in an open-source Python
package SQcircuit. In this manuscript, we introduce the reader to the SQcircuit
environment and functionality. We show through a series of examples how to
analyze a number of interesting quantum circuits and obtain features such as
the spectrum, coherence times, transition matrix elements, coupling operators,
and the phase coordinate representation of eigenfunctions.Comment: 23 pages, 6 figures. Accompanying SQcircuit package on
https://sqcircuit.org
Perfect Intrinsic Squeezing at the Superradiant Phase Transition Critical Point
Some of the most exotic properties of the quantum vacuum are predicted in ultrastrongly coupled photon–atom systems; one such property is quantum squeezing leading to suppressed quantum fluctuations of photons and atoms. This squeezing is unique because (1) it is realized in the ground state of the system and does not require external driving, and (2) the squeezing can be perfect in the sense that quantum fluctuations of certain observables are completely suppressed. Specifically, we investigate the ground state of the Dicke model, which describes atoms collectively coupled to a single photonic mode, and we found that the photon–atom fluctuation vanishes at the onset of the superradiant phase transition in the thermodynamic limit of an infinite number of atoms. Moreover, when a finite number of atoms is considered, the variance of the fluctuation around the critical point asymptotically converges to zero, as the number of atoms is increased. In contrast to the squeezed states of flying photons obtained using standard generation protocols with external driving, the squeezing obtained in the ground state of the ultrastrongly coupled photon–atom systems is resilient against unpredictable noise
Strong dispersive coupling between a mechanical resonator and a fluxonium superconducting qubit
We demonstrate strong dispersive coupling between a fluxonium superconducting
qubit and a 690 megahertz mechanical oscillator, extending the reach of circuit
quantum acousto-dynamics (cQAD) experiments into a new range of frequencies. We
have engineered a qubit-phonon coupling rate of
, and achieved a dispersive interaction that
exceeds the decoherence rates of both systems while the qubit and mechanics are
highly nonresonant (). Leveraging this strong coupling, we
perform phonon number-resolved measurements of the mechanical resonator and
investigate its dissipation and dephasing properties. Our results demonstrate
the potential for fluxonium-based hybrid quantum systems, and a path for
developing new quantum sensing and information processing schemes with phonons
at frequencies below 700 MHz to significantly expand the toolbox of cQAD.Comment: 22 pages, 12 figure