No Arabic abstract
Magnetic resonance with ensembles of electron spins is nowadays performed in frequency ranges up to 240 GHz and in corresponding magnetic fields of up to 10 T. However, experiments with single electron and nuclear spins so far only reach into frequency ranges of several 10 GHz, where existing coplanar waveguide structures for microwave (MW) delivery are compatible with single spin readout techniques (e.g. electrical or optical readout). Here, we explore the frequency range up to 90 GHz, respectively magnetic fields of up to $approx 3,$T for single spin magnetic resonance in conjunction with optical spin readout. To this end, we develop MW resonators with optical single spin access. In our case, rectangular E-band waveguides guarantee low-loss supply of microwaves to the resonators. Three dimensional cavities, as well as coplanar waveguide resonators enhance MW fields by spatial and spectral confinement with a MW efficiency of $1.36,mathrm{mT/sqrt{W}}$. We utilize single NV centers as hosts for optically accessible spins, and show, that their properties regarding optical spin readout known from smaller fields (<0.65 T) are retained up to fields of 3 T. In addition, we demonstrate coherent control of single nuclear spins under these conditions. Furthermore, our results extend the applicable magnetic field range of a single spin magnetic field sensor. Regarding spin based quantum registers, high fields lead to a purer product basis of electron and nuclear spins, which promises improved spin lifetimes. For example, during continuous single-shot readout the $^{14}$N nuclear spin shows second-long longitudinal relaxation times.
Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have been realized and characterized in a wide temperature ($T$, 2-100 K) and magnetic field ($B$, 0-7 T) range. The quality factor $Q_L$ exceeds 10$^4$ below 55 K and it slightly decreases for increasing fields, remaining 90$%$ of $Q_L(B=0)$ for $B=7$ T and $T=2$ K. These features allow the coherent coupling of resonant photons with a spin ensemble at finite temperature and magnetic field. To demonstrate this, collective strong coupling was achieved by using DPPH organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap splitting across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings are observed with a splitting as large as $sim 82$ MHz at $T=2$ K. The spin-cavity collective coupling rate is shown to scale as the square root of the number of active spins in the ensemble.
Using pulsed optically detected magnetic resonance techniques, we directly probe electron-spin resonance transitions in the excited-state of single Nitrogen-Vacancy color centers in diamond. Unambiguous assignment of excited state fine structure is made, based on changes of NV defect photoluminescence lifetime. This study provides significant insight into the structure of the emitting 3E excited state, which is invaluable for the development of diamond-based quantum information processing.
A new method for detecting the magnetic resonance of electronic spins at low temperature is demonstrated. It consists in measuring the signal emitted by the spins with a superconducting qubit that acts as a single-microwave-photon detector, resulting in an enhanced sensitivity. We implement this new type of electron-spin resonance spectroscopy using a hybrid quantum circuit in which a transmon qubit is coupled to a spin ensemble consisting of NV centers in diamond. With this setup we measure the NV center absorption spectrum at 30mK at an excitation level of thicksim15,mu_{B} out of an ensemble of 10^{11} spins.
We investigate the real-time estimation protocols for the frequency shift of optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in nanodiamonds (NDs). Efficiently integrating multipoint ODMR measurements and ND particle tracking into fluorescence microscopy has recently demonstrated stable monitoring of the temperature inside living animals. We analyze the multipoint ODMR measurement techniques (3-, 4-, and 6-point methods) in detail and quantify the amount of measurement artifact owing to several systematic errors derived from instrumental errors of experimental hardware and ODMR spectral shape. We propose a practical approach to minimize the effect of these factors, which allows for measuring accurate temperatures of single NDs during dynamic thermal events. We also discuss integration of noise filters, data estimation protocols, and possible artifacts for further developments in real-time temperature estimation. The present study provides technical details of quantum diamond thermometry and discusses factors that may affect the temperature estimation in biological applications.
We present an experimental and theoretical study of the optically detected magnetic resonance signals for ensembles of negatively charged nitrogen-vacancy (NV) centers in 13C isotopically enriched single-crystal diamond. We observe four broad transition peaks with superimposed sharp features at zero magnetic field and study their dependence on applied magnetic field. A theoretical model that reproduces all qualitative features of these spectra is developed. Understanding the magnetic-resonance spectra of NV centers in isotopically enriched diamond is important for emerging applications in nuclear magnetic resonance.