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Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

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You are here: Home Events Prof. Christopher Kay "Room-Temperature, Solid-State Masers"

Prof. Christopher Kay "Room-Temperature, Solid-State Masers"

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Physical Chemistry and Didactics of Chemistry, Saarland University, Saarbrücken, Germany

What
  • Seminar
When Apr 24, 2019
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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One of the main current uses of masers is for deep space communication, due to their ability to function as extremely low noise amplifiers. However, most masers work under inconvenient conditions, such as low temperatures that require liquid helium for cooling. In this talk, I will discuss our project to build a continuous-wave, solid-state maser based on molecular triplet states and working at room temperature.

Initial experiments used the photo-excited triplet state of pentacene doped into a p-terphenyl single crystal. Anisotropic intersystem crossing to the lowest triplet state with its associated zero-field splitting following pulsed laser excitation creates a population inversion in a pseudo two level system at zero magnetic field. A dielectric (SrTiO3) resonator with a high Purcell factor was designed to enhance the stimulated emission and thus pulsed maser operation was achieved at 1.45 GHz. The kinetics could be modeled using a pair of first-order nonlinear differential equations, often referred to as the Lotka–Volterra or predator–prey equations due to their use in modeling population dynamics in biology [1]. Furthermore, we observed Rabi oscillations in the microwave emission of samples containing a large number of pentacene molecules. This indicates that we have reached a regime in which the spin ensemble and the photons in the microwave resonator mode are strongly coupled. We also observed a cavity protection effect at the onset of the strong-coupling regime that decreases the polariton decay rate as the collective coupling increases [2].

However, a continuous-wave maser is needed for technological applications. We recently achieved this at room temperature by employing NV- centres in diamond which have a triplet (S = 1) ground state (D ~ 2.87 GHz), a 532 nm laser to polarize the electron spins, a dielectric (sapphire) resonator (ν ~ 9.2 GHz) to enhance the stimulated emission and an external magnetic field to tune the resonance via the Zeeman interaction [3].

 [1] E. Salvadori, J.D. Breeze, K.-J. Tan, J. Sathian, B. Richards, M.W. Fung, G. Wolfowicz, M. Oxborrow. N.McN. Alford,N and C.W.M. Kay (2017) Nanosecond time-resolved characterization of a pentacene-based room-temperature MASER. Scientific Reports 7, 41836.

[2] J.D. Breeze, E. Salvadori, N.McN. Alford and C.W.M. Kay. (2017). Room-temperature cavity quantum electrodynamics with strongly coupled Dicke states. npj Quantum Information 3, 40.

[3] J.D. Breeze, E. Salvadori, J. Sathian, N.McN. Alford and C.W.M. Kay (2018). Room-temperature Continuous-wave Diamond Maser. Nature 555, 493-496.

 

invited by Dr. Till Biskup

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