Quantum Microwave Detection with Diamond Spins

Project Information

QuMicro

Grant agreement ID: 101046911

DOI

10.3030/101046911

Project closed

EC signature date 31 March 2022

Start date 1 April 2022

End date 30 September 2025

Funded under

• The European Innovation Council (EIC)

Total cost

€ 2 914 056,00

EU contribution

€ 2 914 056,00

Coordinated by

INTERUNIVERSITAIR MICRO-ELECTRONICA CENTRUM
Belgium

Periodic Reporting for period 2 - QuMicro (Quantum Microwave Detection with Diamond Spins)

Reporting period: 2023-04-01 to 2025-09-30

Summary of the context and overall objectives of the project

The project objectives are as follows:
1) A thorough demonstration of the quantum heterodyne measurement principle.
2) The development of tailored quantum microwave detection protocols usable for commercial applications.
3) A fully self-contained quantum heterodyne microwave detector system technology.
4) Development of entanglement-based sensing methodology.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The three work packages hierarchically encapsulate the novel innovative concept of the proposal to develop quantum heterodyne detection (QHD) of radiofrequency signals that can be used for a wide variety of sensing scenarios, in particular in the project to apply QHD for the detection of RF signals in the high-frequency range, specifically targeting 5G and 6G signals. Unlike the conventional microwave analysers that are on the market and that are based on spectral frequency scans, our concept is based on quantum interferences using Stimulated Raman Adiabatic Passage (STIRAP) protocols which are executed on a matrix of pixels. The number of pixels gives the device’s spectral resolution. This key idea was patented in the project course by the OEAW partner in Austria.
The work of WP1 was focused on the design of the Quantum Heterodyne Detector (QHD) architecture, including diamond equipped with contacts, integration onto PCB with all required microwave components, as well as the detection system and also considerations towards manufacturing of the devices. The microwave detector requires rapid optical switching, readout of multiple sites, and individual microwave control of portions of the detector in order to fulfil the project goals. The consortium has developed solutions for these design challenges and has a complete blueprint for the device architecture ready for implementation. Several PCB’s, designed one-pixel and several-pixel PDMR, have been fabricated to achieve the uniform application of the microwave signal on the diamond sample and minimize the cross-talk between microwaves and the photoelectric detection circuit. All components, including excitation and photo-detection, microwave control, and data acquisition have been implemented. In addition, a comprehensive analysis of various applications for NV-based spectrum analysis and monitoring has been performed. The basic functionality of the detector has been demonstrated and the technical challenges encountered provide a solid basis for future improvements of the microwave detector system.
WP2 has accomplished its goals by engineering diamond material with high coherence times of ~120–150 microseconds for natural-abundance ¹³C samples An advantage of our process is that both the NV and N concentrations are widely tuneable, which allows us to optimise the material specifically for PDMR performance. Furthermore, by optimising the electrical contacts and improving our understanding of depletion-layer properties, and/or by employing graphitic contacts, we succeeded in increasing the photocurrent, which in turn increases the shot-noise limit and therefore improves the SNR. We also improved the detection sensitivity by co-developing specifically designed transimpedance amplifiers and chip boards on which the diamond samples, equipped with electrical contacts, were mounted and tested.
The consortium has achieved significant results on all tasks that make up WP3. The conditions under which spin-to-charge conversion is applicable to shallow NV centers were established and charge-state stability was directly linked to readout performance. In parallel, microwave detection schemes, including QHD, pulsed, and continuous dynamical decoupling, in the presence of diffusion and environmental noise were experimentally compared. The generalized QHD schemes were extended to address the remaining challenge of noise-robustness. We developed a continuous-measurement strategy that exploits temporal correlations in a sensor’s emitted field to retrieve the full quantum Fisher information, surpassing the capabilities of direct photodetection or homodyne detection, and introduced efficient numerical methods for evaluating this information in realistic open sensors. We demonstrated homodyne interferometry with NV centers and further proposed a heterodyne scheme. A widefield photoluminescence scheme for detecting NV-ensemble Rabi oscillations was developed and validated, obtaining close agreement between theoretical modeling and experiment.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

To achieve a wide detection bandwidth, we proposed to use photoelectric detection of magnetic resonances, PDMR, which offers a device approach and potential scalability. This is a breakthrough concept, developed originally by imec, as compared to optical spin readout (ODMR). Finally, the QHD protocols needed to be designed and experimentally verified, which was carried out by the partners from UUlm, both theorists and experimentalists, who designed concrete protocol sequences and experimentally demonstrated them in various sensing environments. Here, it is important to mention that the protocols can be applied to a wide variety of applications in which electromagnetic frequencies are detected, such as NMR. The partners from UUlm have progressed this field in a major way and demonstrated the protocols for detection of NMR signals in spurious noisy environments.
Furthermore, as part of the original proposal, we suggested moving to the unexplored domain of entanglement-based sensing, in which a proof of concept has been demonstrated based on spin-squeezing. Entanglement-based sensing allows Heisenberg scaling, which opens the door to novel concepts in which high sensitivity can be achieved on a limited number of NV spin qubits. To materialise these goals, there were significant challenges, addressing both the preparation of high-coherence-time diamond material, which was uniquely reached in the proposal, by establishing double electron–electron resonance protocols that are directly executed from the NV centre and characterise the surrounding spin bath. This valorisation of our diamonds by tuning their growth conditions, but also electron irradiation and annealing, produced NV centres in a defined manner and at the same time reduced the spin bath. The DEER protocols have been executed both in ODMR and, for the first time, in PDMR mode.
The charge stability and defect study has been executed by the Hungarian partner BME, which in addition modelled new defects such as the group IV–V defects in a large number of published works. Finally, all the components have been brought together in Vienna at OEAW to demonstrate the functional prototypes in chip, equipped with all matrix driving lines, local spot illumination and the STIRAP driving. At the same time, Thales has provided in parallel another driving scheme, using homodyne detection, detecting a phase shift induced by the external fields.
The project covered cross-disciplinary fields from diamond materials, photoelectric readout optimisation, ab-initio NV charge-state optimisation, QD protocol design and theoretical derivation of protocols (including entanglement-based), application to the chips and verification of the original idea.