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We propose a new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultra-narrow clock transition into the mode of a high Q-resonator. The resultant optical radiation has an extremely narrow linewidth in the mHz range, even smaller than that of the clock transition itself due to collective effects. A power level of order $10^{-12}W$ is possible, sufficient for phase-locking a slave optical local oscillator. Realizing this light source has the potential to improve the stability of the best clocks by two orders of magnitude.
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We propose a new type of superradiant laser based on a hot atomic beam traversing an optical cavity. We show that the theoretical minimum linewidth and maximum power are competitive with the best ultracoherent clock lasers. Also, our system operates naturally in continuous wave mode, which has been elusive for superradiant lasers so far. Unlike existing ultracoherent lasers, our design is simple and rugged. This makes it a candidate for the first widely accessible ultracoherent laser, as well as the first to realize sought-after applications of ultracoherent lasers in challenging environments.
We report on the implementation of a high fidelity universal gate-set on optical qubits based on trapped $^{88}$Sr$^+$ ions for the purpose of quantum information processing. All coherent operations were performed using a narrow linewidth diode laser. We employed a master-slave configuration for the laser, where an ultra low expansion glass (ULE) Fabry-Perot cavity is used as a stable reference as well as a spectral filter. We characterized the laser spectrum using the ions with a modified Ramsey sequence which eliminated the affect of the magnetic field noise. We demonstrated high fidelity single qubit gates with individual addressing, based on inhomogeneous micromotion, on a two-ion chain as well as the M{o}lmer-S{o}rensen two-qubit entangling gate.
Due to their high coherence, Lasers are a ubiquitous tool in science. The standard quantum limit for the phase coherence time was first introduced by [A. Schawlow and C. Townes, Phys. Rev. 112, 1940 (1958)], who showed that the minimum possible laser linewidth is determined by the linewidth of the laser cavity divided by twice the number of photons in the cavity. Later, Wiseman showed theoretically that by using Susskind-Glogower (SG) operators to couple the gain medium to the laser cavity it is possible to eliminate pump noise, but not loss noise. This decreases the minimum laser linewidth, though only by a factor of two. In this article, we show that by engineering the coupling between the laser cavity and the output port it is possible to eliminate most of the loss noise as well and construct a laser that has a vastly narrower linewidth, narrower than the standard quantum limit by a factor equal to the number of photons in the laser cavity. We establish a roadmap for building such a device in the laboratory by using Josephson junctions and linear circuit elements to build coupling circuits that behave like SG operators for a range of cavity photon occupancies and using them to couple the laser cavity to both the gain medium and the output port. This device could be an ultra-coherent, cryogenic light source for microwave quantum information experiments. Further, our laser provides highly squeezed light and could be modified to provide designer quantum light which is an important resource for CV/linear optical quantum computing, readout of quantum states in superconducting quantum computers, quantum metrology, and quantum communication. Finally, our proposal relies on the tools and elements of superconducting quantum information, and thus is a clear example of how quantum engineering techniques can inspire us to re-imagine the limits of conventional quantum systems such as the laser.
Nuclear spins of noble gases feature extremely long coherence times but are inaccessible to optical photons. Here we realize a coherent interface between light and noble-gas spins that is mediated by alkali atoms. We demonstrate the optical excitation of the noble-gas spins and observe the coherent back-action on the light in the form of high-contrast two-photon spectra. We report on a record two-photon linewidth of 5$pm$0.7 mHz (millihertz) above room-temperature, corresponding to a one-minute coherence time. This experiment provides a demonstration of coherent bi-directional coupling between light and noble-gas spins, rendering their long-lived spin coherence accessible for manipulations in the optical domain.
A comprehensive investigation of the frequency-noise spectral density of a free-running mid-infrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.
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