Perspective on room-temperature solid-state masers

Abstract

The first solid-state masers to operate at room-temperature and ambient air-pressure were recently demonstrated using optically pumped spin-triplet states as the gain medium. In this Perspective, we briefly review the previous state-of-the-art in cryogenic solid-state masers and then discuss the development of the room-temperature solid-state maser: from the organic pentacene pulsed maser to the diamond nitrogenvacancy continuous-wave maser. We characterize the operation of these masers as coherent microwave sources and ultra-low noise amplifiers before outlining how they can be adapted to act as model systems in which to explore room-temperature cavity quantum electrodynamics. After discussing challenges facing current embodiments of the room-temperature solid-state maser, we explore how they might be addressed or by-passed altogether through the development of alternative materials and masing mechanisms. Finally, we speculate on how the advent of masers that can operate in ambient conditions might lead to novel applications in metrology and quantum technologies.

Diamond-based microwave quantum amplifier

“…[A related concept of maser-based oscillators, operating only at cryogenic temperatures, can be found in (21).] A recent discussion of additional prospects and applications of diamond-based maser oscillators can be found in (22). The most relevant is the potential use in diamond-based sensitive magnetometry (23), where it is possible to boost sensitivity even further due to the extended coherent probing time it provides compared to nonmasing devices.…”

Enhanced quantum sensing with room-temperature solid-state masers

“…In this work, we use the recently developed room-temperature maser (an acronym of microwave amplification by stimulated emission of radiation, i.e., the microwave analog of a laser) (16)(17)(18)(19)(20)(21) for quantum sensing and demonstrate that the threshold behavior and microwave amplification of maser action can be exploited in solid-state ensemble spin sensors for simultaneously addressing both issues mentioned previously. On the basis of an organic solid-state spin system, constituted by photoexcited triplet electron spins of pentacene in p-terphenyl, we realize masing-assisted narrowing of the pentacene-ensemble magnetic resonance line shape, of which halfwidth at half-maximum (HWHM) is substantially reduced to about 130 kHz at room temperature, almost a half of that obtained from a single pentacene molecule at cryogenic temperatures (22).…”

N-Heteroacenes as an Organic Gain Medium for Room-Temperature Masers

“…Organic solid-state masers are an emerging class of ultralow noise amplifiers for microwave signals. − These devices function by exploiting highly spin-polarized triplet states that are formed by spin-selective intersystem crossing (ISC). Interactions between magnetic dipoles of triplet electrons generate a zero-applied magnetic field splitting (ZFS) of spin sublevels (labeled T x , T y , and T z ) characterized by axial |D| and rhombic |E| splitting components.…”

“…For the archetypal organic maser gain material, pentacene-doped p -terphenyl ( Pc :PTP), the triplet state populations (P x :P y :P z ) are 0.76:0.16:0.08, and hence, the most strongly polarized T x –T z transition has been used for masing. , Innovations in resonator technology have reduced the size of zero-applied field (ZF) maser devices significantly and dulcified the requisite operating conditions, however, high signal-to-noise amplification still requires a powerful light source comprising either a Q-switched yellow laser or xenon flash lamp coupled with an invasive Ce:YAG luminescence concentrator. , Even with these innovations, the demonstration of an organic maser operating as a continuous wave (CW) amplifier has remained elusive. Since masers are fundamentally limited by the electron spin dynamics of their gain media, , further work is needed to design maser materials that can operate in miniaturized form and with moderate pumping sources.…”