The development of masers in the 1950s made possible amplifiers that were much quieter than other contemporary amplifiers. An analysis of narrow-band yields a fundamental theorem (Caves theorem) for phase-insensitive linear amplifiers; it requires that such an amplifier, will add noise as large as half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers the theorem establish a lower limit on the product of the noises added to the two phases. In the last decade it was shown theoretically that solid-state masers without inversion may be obtained in multilevel spin systems in dilute paramagnetic solids at high temperature subjected to several strong microwave fields. In the present paper the authors apply the Caves theorem to the maser without inversion in order to find out the best ways in which the proposed device can work.
The development of masers in the 1950s made possible amplifiers that were much quieter than other contemporary amplifiers. An analysis of narrow-band yields a fundamental theorem (Caves theorem) for phase-insensitive linear amplifiers; it requires that such an amplifier, will add noise as large as half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers the theorem establish a lower limit on the product of the noises added to the two phases. In the last decade it was shown theoretically that solid-state masers without inversion may be obtained in multilevel spin systems in dilute paramagnetic solids at high temperature subjected to several strong microwave fields. In the present paper the authors apply the Caves theorem to the maser without inversion in order to find out the best ways in which the proposed device can work.
The development of masers in the 1950's made possible amplifiers that were much quieter than other contemporary amplifiers. An analysis of narrow-band yields a fundamental theorem (Caves theorem) for phase-insensitive linear amplifiers; it requires that such an amplifier, will add noise as large as half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers the theorem establish a lower limit on the product of the noises added to the two phases. In the last decade it was shown theoretically that solid-state masers without inversion may be obtained in multilevel spin systems in dilute paramagnetic solids at high temperature subjected to several strong fields. In the present paper the author applies the Caves theorem to the maser without inversion in order to find out the best ways in which the proposed device can work.
Analytic steady-state solutions of the density-matrix equation are derived by means of a formalism suitable for multilevel spin systems in dilute paramagnetic solids at high temperature and subjected to several strong fields. It is shown that solid-state masers without inversion may be obtained in the presence of one, two, or three quasimonochromatic strong fields at resonance. In the usual cases of two fields, the maser action with or without inversion cannot achieve high-efficiency microwave generation or detection, since for strong emitted fields, the saturating and nonlinear effects are strong too. On the contrary, whenever three frequency-correlated fields fulfill the ``spectroscopic bridge'' conditions, the saturating effects do not occur, and linear effects prevail, even when all these fields are strong. In this case, high-efficiency microwave generations or phase-sensitive detections may be achieved.
Masers once represented the state of the art in low-noise microwave amplification technology but eventually became obsolete due to their need for cryogenic cooling. Masers based on solid-state spin systems perform most effectively as amplifiers, since they provide a large density of spins and can, therefore, operate at relatively high powers. While solid-state maser oscillators have been demonstrated at room temperature, continuous-wave amplification in these systems has only ever been realized at cryogenic temperatures. Here, we report on a continuous-wave solid-state maser amplifier operating at room temperature. We achieve this feat using a practical setup that includes an ensemble of nitrogen-vacancy center spins in a diamond crystal, a strong permanent magnet, and a simple laser diode. We describe important amplifier characteristics including gain, bandwidth, compression power, and noise temperature and discuss the prospects of realizing a room-temperature near-quantum-noise-limited amplifier with this system. Finally, we show that in a different mode of operation the spins can be used to reduce the microwave noise in an external circuit to cryogenic levels, all without the requirement for physical cooling. Published by the American Physical Society 2024
How much noise does quantum mechanics require a linear amplifier to add to a signal it processes? An analysis of narrow-band amplifiers (single-mode input and output) yields a fundamental theorem for phase-insensitive linear amplifiers; it requires such an amplifier, in the limit of high gain, to add noise which, referred to the input, is at least as large as the half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers, which can respond differently to the two quadrature phases ("$cos\ensuremath{\omega}t$" and "$sin\ensuremath{\omega}t$"), the single-mode analysis yields an amplifier uncertainty principle---a lower limit on the product of the noises added to the two phases. A multimode treatment of linear amplifiers generalizes the single-mode analysis to amplifiers with nonzero bandwidth. The results for phase-insensitive amplifiers remain the same, but for phase-sensitive amplifiers there emerge bandwidth-dependent corrections to the single-mode results. Specifically, there is a bandwidth-dependent lower limit on the noise carried by one quadrature phase of a signal and a corresponding lower limit on the noise a high-gain linear amplifier must add to one quadrature phase. Particular attention is focused on developing a multimode description of signals with unequal noise in the two quadrature phases.
Current microwave quantum technologies require the amplification of weak signals with minimal added noise at millikelvin temperatures. To date, this stringent requirement has been met exclusively by superconducting technologies, such as Josephson or kinetic-inductance parametric amplifiers. A fundamentally distinct alternative approach could be offered by masers, the microwave counterpart of lasers, which were predicted as early as the 1950s to achieve quantum-limited noise performance under ideal conditions. However, their dependence on cryogenic operation historically limited further advancement. Here we demonstrate the first-ever non-superconducting, near-quantum-limited maser amplifier operating at millikelvin temperatures utilising nitrogen impurity spins (P1 centres) in diamond. Population inversion is achieved via microwave pumping, exploiting a four-spin cross-relaxation mechanism. We realise a maximum power gain exceeding 30 dB, an added noise of approximately 2.55 quanta above the standard quantum limit, and a maximum 1 dB output compression point of -63 dBm at 6.595 GHz. The ability to operate in strong static magnetic fields of arbitrary orientation may offer a complementary, non-superconducting route for applications such as semiconducting spin-qubit readout, magnetic-resonance spectroscopy, and dark-matter axion searches.
If the uncertainty principle of quantum mechanics is applied to the process of signal measurement, two theorems relating to amplifier noise performance can be deduced. First, it can be shown that it is impossible to construct a linear noiseless amplifier. Second, if the amplifier is characterized as having additive white Gaussian noise, it can be shown that the minimum possible noise temperature of any linear amplifier is T.= In 2 -IIG -hv 1-1/ IG k In the limit of high gain G this expression reduces to that previously derived for the ideal maser and parametric amplifier. It is shown that the minimum noise amplifier does not degrade the signal but rather allows the use of an inaccurate detector to make measurements on an incoming signal to the greatest accuracy consistent with the uncertainty principle.