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Continuous-wave room-temperature diamond maser


The maser—the microwave progenitor of the optical laser—has been confined to relative obscurity owing to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this, it has found application in deep-space communications and radio astronomy owing to its unparalleled performance as a low-noise amplifier and oscillator. The recent demonstration of a room-temperature solid-state maser that utilizes polarized electron populations within the triplet states of photo-excited pentacene molecules in a p-terphenyl host1,2,3 paves the way for a new class of maser. However, p-terphenyl has poor thermal and mechanical properties, and the decay rates of the triplet sublevel of pentacene mean that only pulsed maser operation has been observed in this system. Alternative materials are therefore required to achieve continuous emission: inorganic materials that contain spin defects, such as diamond4,5,6 and silicon carbide7, have been proposed. Here we report a continuous-wave room-temperature maser oscillator using optically pumped nitrogen–vacancy defect centres in diamond. This demonstration highlights the potential of room-temperature solid-state masers for use in a new generation of microwave devices that could find application in medicine, security, sensing and quantum technologies.

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Figure 1: Structure of the NV centres, optical pumping and magnetic-field interaction.
Figure 2: Diamond maser construction.
Figure 3: Electron paramagnetic resonance spectroscopy.
Figure 4: Field-frequency maser emission plots.

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We thank J. Hall and M. Markham (Element 6 Ltd) for supplying the diamond samples, P. French and R. Taylor (Photonics Group at Imperial College London) for lending us their continuous-wave laser, and E. Bauch (Harvard University) for discussions. We also thank M. Lennon (IC), D. Halpin and D. Farquharson (UCL) for manufacturing the cavity components. This work was supported by the UK Engineering and Physical Sciences Research Council through grants EP/K011987/1 (IC) and EP/K011804/1 (UCL). We also acknowledge support from the Henry Royce Institute.

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Authors and Affiliations



J.D.B. conceived the study, developed the theory, designed the maser cavity, devised the experiment and wrote software for collecting experimental data. J.D.B. and C.W.M.K. developed the experimental design and performed experiments with input from E.S. and J.S. J.D.B. interpreted the results with input from E.S. and C.W.M.K. J.S. characterized the diamond NV concentration by optical means and developed the optical pumping scheme. J.D.B., E.S. and C.W.M.K. characterized the diamonds using EPR. J.D.B. wrote the paper with assistance from C.W.M.K. and with additional editing by E.S. and N.M.A.

Corresponding author

Correspondence to Jonathan D. Breeze.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks A. Blank, F. Jelezko and R.-B. Liu for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Diamond sample geometry and orientation.

a, The diamond is a rectangular cuboid with dimensions 2.1 mm × 2.1 mm × 2.6 mm. The main faces (pink) are {100}, with the {111} faces (to which the NV〈111〉 directions are normal) depicted in blue. b, Side view of the diamond oriented within the maser cavity, with static magnetic field B applied across the NV〈111〉 direction. The microwave magnetic field is perpendicular to the N–V defect axis and static magnetic field direction. c, Top view of the diamond when it is oriented inside the cavity. d, Top view of the diamond placed within the single-crystal sapphire ring within the maser cavity. The depiction of the structure of diamond within the crystals (carbon atoms, bonds and tetrahedral) are for illustrative purposes only.

Extended Data Figure 2 Threshold and spin-relaxation measurements.

a, Maser threshold. The peak maser output power increases linearly as a function of the optical pump power (data). Extrapolation of the linear fit (dashed line) to zero maser output power reveals a threshold optical pump power of 138 mW, which is lower than the predicted 180 mW. b, Spin–lattice relaxation time T1 as a function of laser pump power (data). The slight decrease in T1 is expected and due to an increase in temperature caused by the non-radiative (heating) processes during the NV spin-polarizing optical pump cycle. c, Spin-decoherence time T2 as a function of laser pump power (data). There is little change in T2, with a slight jump upon applying optical pumping, probably due to an increase in EPR signal amplitude and hence less error. There is subsequently a slight decrease due to temperature increase and pumping decoherence. Photo-conversion of NV to NV0 could also be a source of decoherence. d, Power saturation broadening. The inhomogeneous spin decoherence time was inferred from power saturation broadening measurements of the spin resonance lines. The spectral full-width at half-maximum (FWHM) γ was measured as a function of interrogating microwave power (data). A spin decoherence rate of was extracted by extrapolating the square of the FWHM linewidth down to zero microwave power (dashed line). The vertical dashed line in b and c depicts the applied optical pump power of 400 mW.

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Breeze, J., Salvadori, E., Sathian, J. et al. Continuous-wave room-temperature diamond maser. Nature 555, 493–496 (2018).

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