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More about Elyjah Kiyooka's research

My contribution to the RobustSuperQ project in the CEA-Pheliqs group is to use experimental techniques in understanding the fundamental characteristics of superconducting-semiconducting heterostructures in the Al-Ge/SiGe material system and using this understanding to define a so-called gatemon qubit (a gate voltage controlled transmon qubit). I investigate super-semi characteristics with different device geometries such as Hall-bars, Josephson junctions, and QPCs close to super-semi interfaces. These allow us to learn about several metrics of: heterostructure qualities including carrier density, and mobility, superconducting qualities such as the superconducting gap, and hybrid properties like the IcRn product, and the interface transparency. Based greatly on the work of a previous PhD student (Chotivut Tangchingchai), I have fabricated and measured some preliminary gatemon qubit devices. I have found these devices to have high Q (~10 000) resonators on SiGe substrate, been able to measure the gatemon qubit anti-crossing with the resonator (shown in left figure), and been able to map the gatemon frequency as a function of gate voltage (shown in right figure). Stay tuned for updates!

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A closer look into Ambroise Peugeot's project

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Dissipation is generally seen as an undesirable phenomenon in physics. This is especially true for quantum systems, where energy loss generally leads to the destruction of state superpositions and the loss of the quantum advantage over classical systems. Much of the work in quantum information is therefore focused on correcting the logical errors brought by the inevitable dissipation in qubits. Interestingly, one of the most promising candidates for quantum information is a qubit that uses dissipation to its advantage. The dissipative cat-qubit is a superconducting resonator that mainly loses energy in the form of photon pairs. This non-classical dissipation mechanism makes it possible to autonomously stabilize quantum superpositions of states, which are greatly protected against "bit-flip" errors. Implementations of the dissipative cat-qubit have already been realized using the standard tools of circuit-QED: ac-driven resonators and Josephson junctions devices. The goal of our project is to propose a different route to implement multi-photon dissipation in a quantum circuit.

May 16th 2023 Marius Villiers joined RobustSuperQ


My research work focuses on the properties of driven superconducting circuits enhanced by Josephson junctions, both theoretically and experimentally. Also, I have strong interest for quantum engineering, meaning the development of tools and components relevant to the integration of quantum systems beyond basic research. In the field of hybrid circuit quantum-electrodynamics (hybrid-cQED), photons hosted in superconducting oscillators are coupled to microscopic systems of various compositions, such as mechanical vibrations, spin ensembles or quantum dots. It was recently proposed to replace the paradigmatic linear LC oscillator used in cQED by a nonlinear one, forced by a detuned parametric drive. The resulting Bogoliubov oscillator (BO) is effectively a harmonic oscillator, whose eigenstates are squeezed Fock states. When coupled to another system, the enhanced fluctuations of the BO eigenstates are expected to boost their interaction strength. My thesis work presented the first demonstration of the squeezing-enhanced coupling of an electromagnetic BO to a superconducting qubit. Owing to the ubiquity of electromagnetic forces, this result opens the way for the integration of BOs with a wide range of microscopic systems. During my PhD I also developed the JAWS sample-holder, a microwave package designed to mitigate the impact of spurious electromagnetic modes on the coherence properties of superconducting circuits. During my one-year postdoc funded by Robust SuperQ, I will work on the experimental challenges surrounding the implementation of a superconducting qubit design protected against decoherence. It includes the optimization of both the fabrication recipe and the microwave environment (thermalization, filtering…), continuing the effort initiated during my PhD with the JAWS package.


Thesis defence Zhiren Wang May 9th 2023

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Single spins in solids are good candidates for implementing quantum bits for quantum information processing thanks to their long coherence times. However, being individual atomic-scale quantum objects, they are difficult to address and to entangle with one another. This thesis work explores two distinct but related approaches for manipulating and detecting single spins, both involving comparable hybrid circuit quantum electrodynamics platforms operated at millikelvin temperatures. In the first approach, single electron spin resonance (ESR) is demonstrated by spin fluorescence detection : a microwave photon counter is used to detect the photon emitted by an excited spin. The spins are paramagnetic erbium ions in a scheelite crystal, and are coupled magnetically to a high-quality factor planar superconducting resonator. They are detected individually with a signal-to-noise ratio of 1.9 in a one second-integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Coherence times up to 3 ms are measured, limited by the engineered spin radiative lifetime. This single-spin quantum control experiment also opens the route to new applications of ESR, in particular for microscopic object characterization. In the second approach, the detection of spins is based on leveraging the charge degree of freedom of hole spins and their strong intrinsic spin-orbit interaction. We demonstrate a compact novel platform made of electrostatically defined quantum dots in AlGaAs/GaAs heterostructure, filled with hole spins by optical illumination. The spins are coupled electrically to a superconducting resonator for probing their charge and spin states. Using this resonator as a dispersive readout, we show that single charge tunneling events in the dots can be detected after illumination. This represents a critical step towards addressing single hole spin in a semiconductor. Overall, the two methods reported in this thesis open new avenues for the development of quantum sensing and quantum computing applications.

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Annual Meeting April 2023 in Grenoble, France

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Quentin Ficheux introduces his project: Superconducting circuits is one of the leading contenders in the race toward practical Quantum computing. The ambition of the project is to exploit the specific features of High-Impedance Superconducting Qubit (HISQ) to outperform the conventional approach based on low-impedance circuits. High-impedance circuits can exhibit record coherence times and their large anharmonicity enable quantum gate operations inspired from atomic systems that have no counterpart in weakly anharmonic systems. In this project, I will study HISQ and exploit their built-in robustness to demonstrate high-coherence times and to push back the limit on the fidelity of Quantum operations.

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