Circuit quantum acoustodynamics with surface acoustic waves

The experimental investigation of quantum devices incorporating mechanical resonators has opened up new frontiers in the study of quantum mechanics at a macroscopic level$^{1,2}$. Superconducting microwave circuits have proven to be a powerful platform for the realisation of such quantum devices, both in cavity optomechanics$^{3,4}$, and circuit quantum electro-dynamics (QED)$^{5,6}$. While most experiments to date have involved localised nanomechanical resonators, it has recently been shown that propagating surface acoustic waves (SAWs) can be piezoelectrically coupled to superconducting qubits$^{7,8}$, and confined in high-quality Fabry-Perot cavities up to microwave frequencies in the quantum regime$^{9}$, indicating the possibility of realising coherent exchange of quantum information between the two systems. Here we present measurements of a device in which a superconducting qubit is embedded in, and interacts with, the acoustic field of a Fabry-Perot SAW cavity on quartz, realising a surface acoustic version of cavity quantum electrodynamics. This quantum acoustodynamics (QAD) architecture may be used to develop new quantum acoustic devices in which quantum information is stored in trapped on-chip surface acoustic wavepackets, and manipulated in ways that are impossible with purely electromagnetic signals, due to the $10^{5}$ times slower speed of travel of the mechanical waves.Comment: 12 pages, 9 figures, 1 tabl

Double-sided coaxial circuit QED with out-of-plane wiring

Superconducting circuits are well established as a strong candidate platform for the development of quantum computing. In order to advance to a practically useful level, architectures are needed which combine arrays of many qubits with selective qubit control and readout, without compromising on coherence. Here we present a coaxial circuit QED architecture in which qubit and resonator are fabricated on opposing sides of a single chip, and control and readout wiring are provided by coaxial wiring running perpendicular to the chip plane. We present characterisation measurements of a fabricated device in good agreement with simulated parameters and demonstrating energy relaxation and dephasing times of $T_1 = 4.1\,\mu$s and $T_2 = 5.7\,\mu$s respectively. The architecture allows for scaling to large arrays of selectively controlled and measured qubits with the advantage of all wiring being out of the plane.Comment: 4 pages, 3 figures, 1 tabl

Simultaneous bistability of qubit and resonator in circuit quantum electrodynamics

We explore the joint activated dynamics exhibited by two quantum degrees of freedom: a cavity mode oscillator which is strongly coupled to a superconducting qubit in the strongly coherently driven dispersive regime. Dynamical simulations and complementary measurements show a range of parameters where both the cavity and the qubit exhibit sudden simultaneous switching between two metastable states. This manifests in ensemble averaged amplitudes of both the cavity and qubit exhibiting a partial coherent cancellation. Transmission measurements of driven microwave cavities coupled to transmon qubits show detailed features which agree with the theory in the regime of simultaneous switching

Critical slowing down in circuit quantum electrodynamics

Critical slowing down of the time it takes a system to reach equilibrium is a key signature of bistability in dissipative first-order phase transitions. Understanding and characterizing this process can shed light on the underlying many-body dynamics that occur close to such a transition. Here, we explore the rich quantum activation dynamics and the appearance of critical slowing down in an engineered superconducting quantum circuit. Specifically, we investigate the intermediate bistable regime of the generalized Jaynes-Cummings Hamiltonian (GJC), realized by a circuit quantum electrodynamics (cQED) system consisting of a transmon qubit coupled to a microwave cavity. We find a previously unidentified regime of quantum activation in which the critical slowing down reaches saturation and, by comparing our experimental results with a range of models, we shed light on the fundamental role played by the qubit in this regime

Extended Esophagectomy in Elderly Patients with Esophageal Cancer: Minor Effect of Age Alone in Determining the Postoperative Course and Survival

Elderly patients who undergo esophagectomy for cancer often have a high prevalence of coexisting diseases, which may adversely affect their postoperative course. We determined the relationship of advanced age (i.e., a parts per thousand yen70 years) with outcome and evaluated age as a selection criterion for surgery. Between January 1991 and January 2007, we performed a curative-intent extended transthoracic esophagectomy in 234 patients with cancer of the esophagus. Patients were divided into two age groups: <70 years (group I; 170 patients) and a parts per thousand yen70 years (group II; 64 patients). Both groups were comparable regarding comorbidity (American Society of Anesthesiologists classification), and tumor and surgical characteristics. The overall in-hospital mortality rate was 6.2% (group I, 5%, vs. group II, 11%, P = 0.09). Advanced age was not a prognostic factor for developing postoperative complications (odds ratio, 1.578; 95% confidence interval, 0.857-2.904; P = 0.143). The overall number of complications was equal with 58% in group I vs. 69% in group II (P = 0.142). Moreover, the occurrence of complications in elderly patients did not influence survival (P = 0.174). Recurrences developed more in patients <70 years (58% vs. 42%, P = 0.028). The overall 5-year survival was 35%, and, when included, postoperative mortality was 33% in both groups (P = 0.676).The presence of comorbidity was an independent prognostic factor for survival (P = 0.002). Advanced age (a parts per thousand yen70 years) has minor influence on postoperative course, recurrent disease, and survival in patients who underwent an extended esophagectomy. Age alone is not a prognostic indicator for survival. We propose that a radical resection should not be withheld in elderly patients with limited frailty and comorbidity

Resistance gene expression determines the in vitro chemosensitivity of non-small cell lung cancer (NSCLC)

Background NSCLC exhibits considerable heterogeneity in its sensitivity to chemotherapy and similar heterogeneity is noted in vitro in a variety of model systems. This study has tested the hypothesis that the molecular basis of the observed in vitro chemosensitivity of NSCLC lies within the known resistance mechanisms inherent to these patients' tumors. Methods The chemosensitivity of a series of 49 NSCLC tumors was assessed using the ATP-based tumor chemosensitivity assay (ATP-TCA) and compared with quantitative expression of resistance genes measured by RT-PCR in a Taqman Array™ following extraction of RNA from formalin-fixed paraffin-embedded (FFPE) tissue. Results There was considerable heterogeneity between tumors within the ATP-TCA, and while this showed no direct correlation with individual gene expression, there was strong correlation of multi-gene signatures for many of the single agents and combinations tested. For instance, docetaxel activity showed some dependence on the expression of drug pumps, while cisplatin activity showed some dependence on DNA repair enzyme expression. Activity of both drugs was influenced more strongly still by the expression of anti- and pro-apoptotic genes by the tumor for both docetaxel and cisplatin. The doublet combinations of cisplatin with gemcitabine and cisplatin with docetaxel showed gene expression signatures incorporating resistance mechanisms for both agents. Conclusion Genes predicted to be involved in known mechanisms drug sensitivity and resistance correlate well with in vitro chemosensitivity and may allow the definition of predictive signatures to guide individualized chemotherapy in lung cancer

Development of a coaxial circuit QED architecture for quantum computing

Superconducting circuit QED is a promising approach for building a quantum computer. In order to realise superconducting circuits at a sufficient scale for useful near-term applications, an architecture with an extensible design is required which implements good connectivity between qubits, and allows for selective readout and control of the qubits without introducing detrimental crosstalk or decoherence. This thesis describes the development of a new coaxial circuit QED architecture that fulfils this requirement of extensibility by incorporating out-of-plane wiring into the sample holder. Single-qubit unit cells consisting of a transmon qubit and readout resonator with coaxial geometries are fabricated on opposing sides of a substrate, and selective control and readout of the qubits is achieved via a capacitance to coaxial wiring built into the device enclosure. Unit cells of qubit and resonator can be arranged in a 2D array without modification of the wiring scheme. A single-qubit unit cell of this architecture is used to implement dispersive circuit QED, and a full characterisation of the Hamiltonian is performed. The device is shown to have parameters comparable to those found in other approaches, such as a coupling between qubit-resonator of ~100 MHz and a coherence time of order ~10 µs. The extension of this scheme to 2D arrays of qubits is then presented, and realizations of two-qubits gates are demonstrated with fidelities all above 87% on a four qubit device. Further evaluations are performed on multi-qubit devices, including a characterisation of the drive isolation of the mode-matched drive ports, finding values in the range of 50 dB and 30 dB for measurement and control respectively. Similarly, the cross coupling between circuits is shown to have values ~2% of the coupling within a unit cell. The effective circuit temperatures are measured, finding typical values of ~100 mK, and the techniques of spin-locking and T2 spectroscopy are employed to probe the noise environment. Finally the architecture is extended to incorporate frequency tuning of qubits with gradiometric SQUID loops by way of off-chip flux bias lines (FBLs). These lines are used to tune qubits with a signal isolation of &gt;99%. Furthermore, the ability of these FBLs to dynamically control the qubit frequency is shown by demonstrating switching of the frequency on a nanosecond time-scale, and parametric driving over a frequency range of gigahertz.</p