Détecteur de photon micro-onde unique à très bas bruit de comptage – DARKWADOR

In the past few years, the quantronics group has focused on hybrid mesoscopic system where superconducting circuits is exploited as a versatile toolbox. High-quality-factor resonators, squeezes and amplifiers have successfully enabled the exploration of new field of mesoscopic physics such as Andreev Bound States in proximitized materials, phase flip dynamics in high kinetic inductance materials or ultra-sensitive electron spin resonance (ESR) of spins embedded in vacancies and defects in high purity crystals. My aim as a new permanent researcher within the quantronics group is to revive research
activities around circuit Quantum electrodynamics based on Josephson circuits and qubits and in particular with the development of qubit-based quantum information processing for advanced quantum sensing. This research direction brings together state-of-the-art fabrication, modeling and concepts I have built up as a young physicist at Berkeley and at ENS. The case of photon
detection is a great example of a fruitful interplay between dissipation engineering, originally introduced in the context of quantum computation and advanced sensing techniques. In particular, in this proposal, we show how basic level of quantum error correction can be introduced within
a detection scheme in order to mitigate noise of the detector and further reduce dark count rates following the ideas introduced by Lescanne et al. This cutting edge sensing apparatus will be of great interest for the exploration of hybrid mesocopic systems in the Quantronics group and noticeably for quantum information processing.

For a general purpose microwave photon detector, the operating frequency of the detector should be matched with the source and the bandwidth should be large enough compared to the emitter line-width. For frequency tunability, a SQUID array will be incorporated into the input resonator. By threading magnetic within the SQUID loop, the effective inductance varies, and hence the resonant frequency of the microwave LC cavity shifts. Frequency uncertainty due to fabrication is of the order of 100 MHz, therefore the detector should be tunable at least over that range. Note that the design parameters require some level of fine tuning to reach optimal detection performances at a given frequency. Hence, a realistic design will be constrained within a frequency range of 5% of the nominal resonator frequency (~ 5 GHz). Second, Purcell filters must be placed at both ends of the circuits in order to increase the detection bandwidth. Owing to the frequency selectivity of such filters, they allow for large coupling of resonators to lines while inhibiting the direct relaxation of the qubit placed far off-resonance. Finally, state-of-the-art fabrication techniques will be investigated such as trenching of the dielectric below the superconducting resonators in order to decrease dielectric losses and therefore increase the overall performance of the circuit.

This project explores a new paradigm for quantum information processing in metrology and sensing. In the future, the technology developed here could be at the heart of novel detection schemes in uncharted territory of the electromagnetic spectrum. In a longer run, it could be a key device for modular and hybrid architecture for quantum information processing as quantum computing.

DARKWADOR aims at the creation and development of a general purpose Single Microwave Photon Detector whose performance will be on par with state-of-the-art optical detectors. Microwave photon detectors are increasingly sought-after due to their applications in measurement based quantum computing, dark matter axions detection, electron-paramagnetic-resonance spectroscopy, or quantum-enhanced imaging. However such experimental
proposal in the microwave domain have been hindered by the unavailability of low dark-count photon detectors. The research direction proposed is both novel and cutting edge. It deals with the newly developed superconducting circuits toolbox for quantum information processing. In particular, quantum dissipation engineering and quantum error mitigation lie at the heart of this proposal. The exquisite level of control pursued in this project would hence have an impact on a variety of highly innovative and relevant technological fields. In this context, let us note that major industrial actors in the field of high-tech information systems, such as Google, IBM, and institutions like NASA massively invest in quantum computer research based on superconducting technology. The proposed Single Microwave Photon Detector will give rise to patents and applications. A practical version of the detector with unprecedented dark count rate could overwhelm quantum-enhanced sensing in the microwave domain, similarly to Josephson Parametric Amplifier which are today ubiquitous and commercially available. On similar grounds, this project could lead to the creation of a start-up, commercializing high-performance photon detector for the quantum computing community and quantum sensing for astrophysics application and beyond.