14 research outputs found
Stabilizing Rabi Oscillation of a Charge Qubit via Atomic Clock Technique
We propose a superconducting circuit-atom hybrid, where the Rabi oscillation
of single excess Cooper pair in the island is stabilized via the common
atomic-clock technique. The noise in the superconducting circuit is mapped onto
the voltage source which biases the Cooper-pair box via an inductor and a gate
capacitor. The fast fluctuations of the gate charge are significantly
suppressed by an inductor-capacitor resonator, leading to a
long-relaxation-time Rabi oscillation. More importantly, the residual
low-frequency fluctuations are further reduced by using the general
feedback-control method, in which the voltage bias is stabilized via
continuously measuring the dc-Stark-shift-induced atomic Ramsey signal. The
stability and coherence time of the resulting charge-qubit Rabi oscillation are
both enhanced. The principal structure of this Cooper-pair-box oscillator is
studied in detail.Comment: 4 figure
Superconducting Resonator-Rydberg Atom Hybrid in the Strong Coupling Regime
We propose a promising hybrid quantum system, where a highly-excited atom
strongly interacts with a superconducting LC oscillator via the electric field
of capacitor. An external electrostatic field is applied to tune the energy
spectrum of atom. The atomic qubit is implemented by two eigenstates near an
avoided-level crossing in the DC Stark map of Rydberg atom. Varying the
electrostatic field brings the atomic-qubit transition on- or off-resonance to
the microwave resonator, leading to a strong atom-resonator coupling with an
extremely large cooperativity. Like the nonlinearity induced by Josephson
junctions in superconducting circuits, the large atom-resonator interface
disturbs the harmonic potential of resonator, resulting in an artificial
two-level particle. Different universal two-qubit logic gates can also be
performed on our hybrid system within the space where an atomic qubit couples
to a single photon with an interaction strength much larger than any relaxation
rates, opening the door to the cavity-mediated state transmission.Comment: 4 figure
Correlation of Left Ventricular Myocardial Work Indices with Invasive Measurement of Stroke Work in Patients with Advanced Heart Failure
ObjectivesThis study aimed to explore the correlation between left ventricular (LV) myocardial work (MW) indices and invasively-derived LV stroke work index (SWI) in a cohort of patients with advanced heart failure (AHF) considered for heart transplantation. BackgroundLeft ventricular MW has emerged as a promising tool for diagnostic and prognostic purposes in heart failure (HF) but its relationship with hemodynamic data derived from right heart catheterization (RHC) has not been assessed in patients with advanced heart failure yet. Materials and methodsConsecutive patients with AHF considered for heart transplantation from 2016 to 2021 performing RHC and echocardiography as part of the workup were included. Conventional LV functional parameters and LV MW indices, including LV global work index (GWI), LV global constructive work (GCW), LV global wasted work (GWW), LV global work efficiency (GWE), and other were calculated and compared with invasively-measured LV SWI. ResultsThe population included 44 patients. Median time between RHC and echocardiography was 0 days (IQR: 0-24). Median age was 60 years (IQR: 54-63). For the most part, etiology of HF was non-ischemic (61.4%) and all patients were either on class NYHA II (61.4%) or III (27.3%). Median left ventricular ejection fraction was 25% (IQR: 22.3-32.3), median NT-proBNP 1,377 pg/ml (IQR: 646-2570). LV global longitudinal strain (GLS) significantly correlated with LV SWI (r = -0.337; p = 0.031), whereas, LV ejection fraction (EF) did not (r = 0.308; p = 0.050). With regard to LV MW indices, some of them demonstrated correlation with LV SWI, particularly LV GWI (r = 0.425; p = 0.006), LV GCW (r = 0.506; p = 0.001), LV global positive work (LV GPW; r = 0.464; p = 0.003) and LV global systolic constructive work (GSCW; r = 0.471; p = 0.002). ConclusionAmong LV MW indices, LV GCW correlated better with invasively-derived SWI, potentially representing a powerful tool for a more comprehensive evaluation of myocardial function
AN EXPERIMENTAL PLATFORM FOR HYBRIDIZATION OF ATOMIC AND SUPERCONDUCTING QUANTUM SYSTEMS
Ph.DDOCTOR OF PHILOSOPHY (CQT
Superconducting atom chips : towards quantum hybridization
Atomic-superconducting hybrid systems are of particular interest as they are combining the long coherence times of ultracold atoms and fast gate operation times of superconducting circuits. Here we discuss an experimental realization of an interface between cold Rydberg atoms and a transmon circuit embedded in a microwave cavity. We present numerical calculations showing a significant coupling of Rydberg atoms to a transmon. Here we place the atoms in the vicinity of the transmon shunting capacitor. Exciting them to the Rydberg states alters the dielectric constant of the medium inside the capacitor. This results in a dispersive shift of the transmon resonance frequency. Using the protocols developed in Ref. 1, 2 will allow the coherent transfer of quantum states between these two systems.NRF (Natl Research Foundation, S’pore)Published versio
Ghost factors in Gauss-sum factorization with transmon qubits
A challenge in the Gauss sums factorization scheme is the presence of ghost
factors - non-factors that behave similarly to actual factors of an integer -
which might lead to the misidentification of non-factors as factors or vice
versa, especially in the presence of noise. We investigate Type II ghost
factors, which are the class of ghost factors that cannot be suppressed with
techniques previously laid out in the literature. The presence of Type II ghost
factors and the coherence time of the qubit set an upper limit for the total
experiment time, and hence the largest factorizable number with this scheme.
Discernability is a figure of merit introduced to characterize this behavior.
We introduce preprocessing as a strategy to increase the discernability of a
system, and demonstrate the technique with a transmon qubit. This can bring the
total experiment time of the system closer to its decoherence limit, and
increase the largest factorizable number.Comment: 14 pages, 8 figures, 2 appendice
Design of an experimental platform for hybridization of atomic and superconducting quantum systems
Hybrid quantum systems have the potential of mitigating current challenges in developing a scalable quantum computer. Of particular interest is the hybridization between atomic and superconducting qubits. We demonstrate an experimental setup for transferring and trapping ultracold atoms inside a millikelvin cryogenic environment, where interactions between atomic and superconducting qubits may be established, paving the way for hybrid quantum systems. We prepare Rb87 atoms in a conventional magneto-optical trap and transport them via a magnetic conveyor belt into a UHV compatible dilution refrigerator with optical access. We store 5×108 atoms with a lifetime of 794 s in the vicinity of the millikelvin stage