13 research outputs found
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
Magnetically Tuned Continuous Transition from Weak to Strong Coupling in Terahertz Magnon Polaritons
Depending on the relative rates of coupling and dissipation, a light-matter coupled system is either in the weak- or strong-coupling regime. Here, we present a unique system where the coupling rate continuously increases with an externally applied magnetic field while the dissipation rate remains constant, allowing us to monitor a weak-to-strong coupling transition as a function of magnetic field. We observed a Rabi splitting of a terahertz magnon mode in yttrium orthoferrite above a threshold magnetic field of ~ 14 T. Based on a microscopic theoretical model, we show that with increasing magnetic field the magnons transition into magnon polaritons through an exceptional point, which will open up new opportunities for in situ control of non-Hermitian systems
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
Ultrastrong magnon-magnon coupling dominated by antiresonant interactions
Makihara T, Hayashida K, Noe Ii GT, et al. Ultrastrong magnon-magnon coupling dominated by antiresonant interactions. Nature communications. 2021;12(1): 3115.Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics systems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations owing to antiresonant terms in the Hamiltonian. However, such predictions have not been realized because antiresonant interactions are typically negligible compared to resonant interactions in light-matter systems. Here we report an unusual, ultrastrongly coupled matter-matter system of magnons that is analytically described by a unique Hamiltonian in which the relative importance of resonant and antiresonant interactions can be easily tuned and the latter can be made vastly dominant. We found a regime where vacuum Bloch-Siegert shifts, the hallmark of antiresonant interactions, greatly exceed analogous frequency shifts from resonant interactions. Further, we theoretically explored the system's ground state and calculated up to 5.9 dB of quantum fluctuation suppression. These observations demonstrate that magnonic systems provide an ideal platform for exploring exotic quantum vacuum phenomena predicted in ultrastrongly coupled light-matter systems