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arXiv:2507.01328

Superradiant Echoes Induced by Multiple Re-phasing of NV Spin Sub-ensembles Grating at Room Temperature

Qilong Wu, Yuan Zhang, Huihui Yu, Chongxin Shan, Klaus Mølmer

Published Jul 2, 2025• 0 citations
arXivHTMLPDF

Abstract

In this Letter, we propose that superradiant echoes can be achieved at room temperature by applying a laser illumination and a microwave Hahn echo sequence to a diamond with a high concentration of nitrogen-vacancy (NV) centers placed in a dielectric microwave cavity. We identify that the combined action of two microwave driving pulses and a free evolution imprints a phase grating among NV spin sub-ensembles in frequency space, and multiple re-phasing of the grated spin sub-ensembles leads to multiple superradiant echoes through a collective coupling with the cavity. Furthermore, we show that the superradiant echoes can be actively tailored with the microwave pulses and the laser illumination by modifying the grating parameters, and the multiple re-phasing dynamics is analogous to the one leading to superradiant beats in optical clock system. In the future, the spin sub-ensembles grating and the resulting echoes can be further optimized with dynamical decoupling, which might pave the way for applications in quantum sensing.

DOI
10.48550/arxiv.2507.01328

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In this Letter, we propose that superradiant echoes can be achieved at room temperature by applying a laser illumination and a microwave Hahn echo sequence to a diamond with a high concentration of nitrogen-vacancy (NV) centers placed in a dielectric microwave cavity. We identify that the combined action of two microwave driving pulses and a free evolution imprints a phase grating among NV spin sub-ensembles in frequency space, and multiple re-phasing of the grated spin sub-ensembles leads to multiple superradiant echoes through a collective coupling with the cavity. Furthermore, we show that the superradiant echoes can be actively tailored with the microwave pulses and the laser illumination by modifying the grating parameters, and the multiple re-phasing dynamics is analogous to the one leading to superradiant beats in optical clock system. In the future, the spin sub-ensembles grating and the resulting echoes can be further optimized with dynamical decoupling, which might pave the way for applications in quantum sensing.
Magnetic resonance can be used as a testbed for observing, demonstrating, and studying fundamental concepts of quantum cavity interaction with a two-level system at the microwave regime. Such experiments are mostly carried out at low cryogenic temperatures with spin systems that are embedded in a high-quality (Q-factor) superconducting cavity. For example, recent work has shown that under such conditions, and in a regime of high cooperativity and strong collective coupling between an electron spin system and a microwave cavity, multiple spin echoes are observed. These echoes have been analysed as signatures of coherent quantum effects; namely, the photons in the cavity can excite the spin system, which in turn can excite the cavity itself and so on. In this work we show that the use of a unique tailor-made moderate Q cavity in conjunction with diamond crystals having large concentrations of nitrogen vacancy (NV) centers makes it possible to observe such non-linear quantum phenomenon, even at room temperature. A key requirement of our experiments is that the spin system’s thermodynamic (rather than the physical) temperature is cooled to a few K, while high cooperativity and/or strong coupling are not a necessary prerequisite for such observations. The observation of meaningful microwave cavity quantum effects even at room temperature could lead to applications such as quantum memories and quantum sensing.
Recent experiments demonstrated the cooling of a microwave mode of a high-quality dielectric resonator coupled to optically cooled nitrogen-vacancy (NV) spins in diamond. Our recent theoretical study [arXiv:2110.10950] pointed out the cooled NV spins can be used to realize cavity quantum electrodynamics effects (C-QED) at room temperature. In this article, we propose to modify the setup used in a recent diamond maser experiment [Nature 55, 493-496 (2018)], which features a higher spin transition frequency, a lower spin-dephasing rate and a stronger NV spins-resonator coupling, to realize better microwave mode cooling and the room-temperature CQED effects. To describe more precisely the optical spin cooling and the collective spin-resonator coupling, we extend the standard Jaynes-Cumming model to account for the rich electronic and spin levels of the NV centers. Our calculations show that for the proposed setup it is possible to cool the microwave mode from 293293293 K (room temperature) to 116116116 K, which is about 727272 K lower than the previous records, and to study the intriguing dynamics of the CQED effects under the weak-to-strong coupling transition by varying the laser power. With simple modifications, our model can be applied to, e.g., other solid-state spins or triplet spins of pentacene molecules, and to investigate other effects, such as the operations of pulsed and continuous-wave masing.
Nitrogen-vacancy (NV) centers in diamond as ideally individual spin quantum systems can be coherently manipulated by microwave fields. Compared to the traditional method using the IQ (In-phase/Quadrature) mixer with a local oscillator and intermediate-frequency (IF) signals, we report an effective and technically simple method to generate the required microwave field by frequency multiplication and realize coherent manipulation of the NV center’s electron spin. After frequency multiplication, the IF signal can be directly converted to the high-frequency microwave field with adjustable pulse width, frequency, phase, and amplitude. A series of spin dynamics applications such as Rabi oscillation, free induction decay, and spin-locking are executed, which verified its performance and feasibility. Frequency multiplication can overcome the problem of clock synchronization between the local oscillator and IF signal and greatly reduce the complexity of the experimental system. The method can be easily used to realize a more complex quantum control sequence such as dynamic decoupling and extended to a wide range of spin-based quantum information applications in the future.
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Coherent coupling between optical fields and solid-state spins is essential for building a spin–photon interface and exchanging quantum information. The nitrogen-vacancy (NV) center, a solid-state defect center in diamond, is a promising qubit system for its relatively high-temperature spin coherence. Here, we study the coherent coupling between the photonic spin texture (PST) and the quantum polarization cloud (phase shift) of NV centers spanning a temperature range from liquid nitrogen (77 K) to room temperature (295 K). We show that by optimizing the laser power and frequency detuning, it is possible to maintain coherence in NV–photon interaction even in this nonideal limit. The coherent NV–photon interaction in our experiment is encoded in the quantum phase shift of the NV center spin qubit, which can be read out using the Hahn-echo magnetometry technique. Our approach of studying light–matter interaction at an elevated temperature can build an unexplored regime of spin–photon interface, which has potential applications in diverse quantum applications.