High-finesse Optical Cavity Research Articles

Emergent limit cycles and time crystal dynamics in an atom-cavity system

We propose an experimental realization of a time crystal using an atomic Bose-Einstein condensate in a high finesse optical cavity pumped with laser light detuned to the blue side of the relevant atomic resonance. By mapping out the dynamical phase diagram, we identify regions in parameter space showing stable limit cycle dynamics. Since the model describing the system is time-independent, the emergence of a limit cycle phase indicates the breaking of continuous time translation symmetry. Employing a semiclassical analysis to demonstrate the robustness of the limit cycles against perturbations and quantum fluctuations, we establish the emergence of a time crystal.

Probing Planck-scale spacetime by cavity opto-atomic $^{87}$Rb interferometry

The project of \emph{"quantum spacetime phenomenology"} focuses on searching pragmatically for the Planck scale quantum features of spacetime. Among these features is the existence of a characteristic length scale addressed commonly by effective approaches to quantum gravity (QG). This characteristic length scale could be realized, for instance and simply, by generalizing the standard Heisenberg uncertainty principle (HUP) to a \emph{"generalized uncertainty principle"} (GUP). While usually it is expected that phenomena belonging to the realm of QG are essentially probable solely at the so-called Planck energy, here we show how a GUP proposal containing the most general modification of coordinate representation of the momentum operator could be probed by a \emph{"cold atomic ensemble recoil experiment"} (CARE) as a low energy quantum system. This proposed atomic interferometer setup has advantages over the conventional architectures owing to the enclosure in a high finesse optical cavity which is supported by a new class of low power consumption integrated devices known as \emph{"micro-electro-opto-mechanical systems"} (MEOMS). The proposed system comprises of a micro mechanical oscillator instead of spherical confocal mirrors as one of the components of high finesse optical cavity. In the framework of a bottom-up QG phenomenological viewpoint and by taking into account the measurement accuracy realized for the fine structure constant (FSC) from the Rubidium ($^{87}$Rb) CARE, we set some constraints as upper bounds on the characteristic parameters of the underlying GUP. In the case of superposition of the possible GUP modification terms, we managed to set a tight constraint as $0.999978<\lambda_0<1.00002$ for the dimensionless characteristic parameter.

Lamb-dip spectroscopy of buffer-gas-cooled molecules

Nowadays, buffer-gas cooling represents an invaluable option to produce cold stable molecules, both in view of secondary cooling/trapping strategies towards the achievement of quantum degeneracy and for fundamental studies of complex molecules. From this follows a demand to establish a pool of specialized, increasingly precise spectroscopic interrogation techniques. Here, we demonstrate a general approach to Lamb-dip ro-vibrational spectroscopy of buffer-gas-cooled molecules. The saturation intensity of the selected molecular transition is achieved by coupling the probe laser to a high-finesse optical cavity surrounding the cold sample. A cavity ring-down technique is then implemented to perform saturation sub-Doppler measurements as the buffer (He) and molecular gas flux are varied. As an example, the (ν1+ν3) R(1) ro-vibrational line in a 20 Kelvin acetylene sample is addressed. By referencing the probe laser to a Rb/GPS clock, the corresponding line-center frequency as well as the self and foreign (i.e., due to the buffer gas) collisional broadening coefficients are absolutely determined. Our approach represents an important step towards the development of a novel method to perform ultra-precise ro-vibrational spectroscopy on an extremely wide range of cold molecules. In this respect, we finally discuss a number of relevant upgrades underway in the experimental setup to considerably improve the ultimate spectroscopic performance.

Ultrasensitive photoacoustic detection in a high-finesse cavity with Pound-Drever-Hall locking.

We demonstrate an ultrasensitive photoacoustic sensor using a low laser power (4mW) and high-finesse (>9000) optical cavity. The Pound-Drever-Hall (PDH) method is adopted to lock the external cavity diode laser at 1531.58nm to the Fabry-Pérot cavity. By placing a photoacoustic cell inside the 130-mm-long optical cavity, we obtain an enhancement of more than 630 times in laser power for acetylene (C2H2) detection. The present photoacoustic spectroscopy (PAS) sensor achieves a normalized noise equivalent absorption coefficient of 1.1×10-11 cm-1 WHz-1/2, which is unprecedented sensitivity among all the current PAS sensors. Our results demonstrate the feasibility of merging PAS with a high-finesse cavity using PDH locking for ultrasensitive trace gas detection.

Cavity enhanced measurement of trap frequency in an optical dipole trap**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304502), the National Natural Science Foundation of China (Grant Nos. 11634008, 11674203, 11574187, and 61227902), and the Fund for Shanxi “1331 Project” Key Subjects Construction.

We demonstrate a direct, fluorescence-free measurement of the oscillation frequency of cold atoms in an optical dipole trap based on a high-finesse optical cavity strongly coupled to atoms. The parametric heating spectra of the trapped atoms are obtained by recording the transmitted photons from the cavity with the trap depth is modulated by different frequency. Moreover, in our method the oscillation can be observed directly in the time scale. Being compared to the conventional fluorescence-dependent method, our approach avoids uncertainties associated with the illuminating light and auxiliary imaging optics. This method has the potential application of determining the motion of atoms with stored quantum bits or degenerate gases without destroying them.

Rapid Production of Many-Body Entanglement in Spin-1 Atoms via Cavity Output Photon Counting.

We propose a simple and efficient method for generating metrologically useful quantum entanglement in an ensemble of spin-1 atoms that interacts with a high-finesse optical cavity mode. It requires straightforward preparation of N atoms in the m_{F}=0 sublevel, tailoring of the atom-field interaction to give an effective Tavis-Cummings model for the collective spin-1 ensemble, and a photon counting measurement on the cavity output field. The photon number provides a projective measurement of the collective spin length S, which, for the chosen initial state, is heavily weighted around values S≃sqrt[N], for which the corresponding spin states are strongly entangled and exhibit Heisenberg scaling of the metrological sensitivity with N, as quantified by the quantum Fisher information.

Polarization Oscillations in Birefringent Emitter-Cavity Systems.

We present the effects of resonator birefringence on the cavity-enhanced interfacing of quantum states of light and matter, including the first observation of single photons with a time-dependent polarization state that evolves within their coherence time. A theoretical model is introduced and experimentally verified by the modified polarization of temporally long single photons emitted from a ^{87}Rb atom coupled to a high-finesse optical cavity by a vacuum-stimulated Raman adiabatic passage process. Further theoretical investigation shows how a change in cavity birefringence can both impact the atom-cavity coupling and engender starkly different polarization behavior in the emitted photons. With polarization a key resource for encoding quantum states of light and modern micron-scale cavities particularly prone to birefringence, the consideration of these effects is vital to the faithful realization of efficient and coherent emitter-photon interfaces for distributed quantum networking and communications.

Multimode interferometry for entangling atoms in quantum networks

We bring together a cavity-enhanced light–matter interface with a multimode interferometer (MMI) integrated onto a photonic chip and demonstrate the potential of such hybrid systems to tailor distributed entanglement in a quantum network. The MMI is operated with pairs of narrowband photons produced a priori deterministically from a single 87Rb atom strongly coupled to a high-finesse optical cavity. Non-classical coincidences between photon detection events show no loss of coherence when interfering pairs of these photons through the MMI in comparison to the two-photon visibility directly measured using Hong–Ou–Mandel interference on a beam splitter. This demonstrates the ability of integrated multimode circuits to mediate the entanglement of remote stationary nodes in a quantum network interlinked by photonic qubits.

Optical bistability and nonlinear dynamics by saturation of cold Yb atoms in a cavity

We observed optical bistability as well as oscillations in the upper bistable branch when cold ytterbium atoms are dispersively coupled to a high finesse optical cavity. Comparable previous observations were explained by atomic density oscillations in case of a Bose-Einstein-Condensate or optical pumping in case of a cold cloud of cesium. Both explanations do not apply in our case of thermal atoms with only a single ground state. We propose a simple two-level model including saturation to describe our experimental results. This paper introduces the experimental setup, derives the mentioned model and compares it to our experimental data. Good quantitative agreement supports our model.

Real-time vibrations of a carbon nanotube

The field of miniature mechanical oscillators is rapidly evolving, with emerging applications including signal processing, biological detection1 and fundamental tests of quantum mechanics2. As the dimensions of a mechanical oscillator shrink to the molecular scale, such as in a carbon nanotube resonator3-7, their vibrations become increasingly coupled and strongly interacting8,9 until even weakthermal fluctuations could make the oscillator nonlinear10-13. The mechanics at this scale possesses rich dynamics, unexplored because an efficient way of detecting the motion in real time is lacking. Here we directly measure the thermal vibrations of a carbon nanotube in real time using a high-finesse micrometre-scale silicon nitride optical cavity as a sensitive photonic microscope. With the high displacement sensitivity of 700fmHz-1/2 and the fine time resolution of this technique, we were able to discover a realm of dynamics undetected by previous time-averaged measurements and a room-temperature coherence that is nearly three orders of magnitude longer than previously reported. We find that the discrepancy in the coherence stems from long-time non-equilibrium dynamics, analogous to the Fermi-Pasta-Ulam-Tsingou recurrence seen in nonlinear systems14. Our data unveil the emergence of a weakly chaotic mechanical breather15, in which vibrational energy is recurrently shared among several resonance modes-dynamics that we are able to reproduce using a simple numerical model. These experiments open up the study of nonlinear mechanical systems in the Brownian limit (that is, when a system is driven solely by thermal fluctuations) and present an integrated, sensitive, high-bandwidth nanophotonic interface for carbon nanotube resonators.

Preparing the spin-singlet state of a spinor gas in an optical cavity

We propose a method to prepare the spin singlet in an ensemble of integer-spin atoms confined within a high-finesse optical cavity. Using a cavity-assisted Raman transition to produce an effective Tavis-Cummings model, we show that a high fidelity spin singlet can be produced probabilistically, although with low efficiency, heralded by the \emph{absence} of photons escaping the cavity. In a different limit, a similar configuration of laser and cavity fields can be used to engineer a model that emulates spinor collisional dynamics. Borrowing from techniques used in spinor Bose-Einstein condensates, we show that adiabatic transformation of the system Hamiltonian (via a time-dependent, effective quadratic Zeeman shift) can be used to produce a low fidelity spin singlet. Then, by following this method with the aforementioned heralding technique, we show that it is possible to prepare the singlet state with both high fidelity and good efficiency for a large ensemble.

Broadband coherent cavity-enhanced dual-comb spectroscopy

Cavity-enhanced spectroscopic instruments impact a broad range of scientific fields because they are sensitive, self-contained, and can be packaged for use by nonspecialists. Infrared-laser-based cavity-enhanced instruments are typically limited to measuring a few small molecules because they rely on narrowly tunable lasers that each measure a molecular transition. Broadband dual-comb spectroscopy (DCS) is a spectroscopic technique capable of simultaneously probing molecular absorption on thousands of narrowly spaced wavelengths using a single high-speed photodetector. With coherent averaging, DCS can measure multiple species, including large molecules, with a high signal-to-noise ratio (SNR). Here, we lock a high-finesse optical cavity to a broadband mode-locked frequency comb with an approach that enables a high SNR, broadband cavity-enhanced DCS with coherent averaging. With a 7.5 cm optical cavity, we attain a >12,000× path-length-enhancement factor, 60 nm bandwidth near 1660 nm (3.5% fractional bandwidth), and >27 dB SNR in 160 s. We measure the dense rovibrational spectrum of ethane in a background of overlapping H2O, CH4, and CO2 absorption. By combining the broadband, high-resolution, and single-detector nature of DCS with a compact optical cavity, we enable future self-contained instruments that are able to simultaneously detect a variety of molecules in realistic ambient conditions.

Three methods for characterizing thermo-optic noise in optical cavities

Thermo-optic noise is likely to be the dominant noise source in next generation ultralow noise optical cavities. We developed three measurement and analysis methods, allowing us to estimate the level of coating thermo-optic noise in optical cavities, including interferometric gravitational wave detectors. We measured the shift in the broadband transmission spectra as a function of temperature for single-layer, high index coatings in order to find the thermo-optic coefficient, ${\ensuremath{\beta}}_{H}$, of a coating while assuming the thermal expansion coefficient, ${\ensuremath{\alpha}}_{H}$. Our value for ${\ensuremath{\beta}}_{H}$ could then be used to calculate the thermo-optic noise in any high-finesse optical cavity using coatings with the same high index layer material. We also measured the spectra as a function of temperature of a multilayer, high-reflectivity coating where the material composition of the layers was similar to the coatings installed in Advanced LIGO. This method has the advantage of allowing us to calculate thermo-optic noise directly; ${\ensuremath{\alpha}}_{H}$ and ${\ensuremath{\beta}}_{H}$ do not need to be known separately, although we do need to know the value of the overall coating thermal expansion coefficient. Finally, we used lasers of different wavelengths to measure transmission changes on the band edges of a multilayer high-reflectivity coating. This gave measurements with high statistical precision but potentially lower systematic accuracy. To address systematic accuracy concerns, we used a constrained Monte Carlo application of the theory of multilayer coating transmission.

Single-particle localization in dynamical potentials

Single particle localization of an ultra-cold atom is studied in one dimension when the atom is confined by an optical lattice and by the incommensurate potential of a high-finesse optical cavity. In the strong coupling regime the atom is a dynamical refractive medium, the cavity resonance depends on the atomic position within the standing-wave mode and nonlinearly determines the depth and form of the incommensurate potential. We show that the particular form of the quasi-random cavity potential leads to the appearance of mobility edges, even in presence of nearest-neighbour hopping. We provide a detailed characterization of the system as a function of its parameters and in particular of the strength of the atom-cavity coupling, which controls the functional form of the cavity potential. For strong atom-photon coupling the properties of the mobility edges significantly depend on the ratio between the periodicities of the confining optical lattice and of the cavity field.

A single external cavity laser-based sensor for simultaneous detection and quantification of atmospheric methane and water vapor

A single external cavity diode laser (ECDL)-based sensor system was developed for simultaneous measurements of methane and water vapor in the atmospheric air. A home-made continuous wave (CW) ECDL with a wavelength of $$\sim$$ 1325 nm was employed to cover two absorption lines for different gas species. A high-finesse optical cavity composed of two high-reflectivity mirrors ( $$R=0.99927$$ ) was used to enhance the gas absorption in a space of 0.5 l. An isolated methane absorption line at $$7552.74 \hbox { cm}^{-1}$$ and a common (non-isolated) absorption line of water vapor and methane $$7552.81\hbox {cm}^{-1}$$ were utilized for simultaneous detection. A method was developed to calculate the water vapor concentration from these lines. To our knowledge, the method and the absorption lines used in the present paper were used for the first time for simultaneous measurement of the concentrations of atmospheric methane and water vapor.

Deterministic quantum state transfer between remote atoms with photon-number superposition states

We propose a protocol for quantum networking based on deterministic quantum state transfer between distant memory nodes using photon-number superposition states (PNSS). In the suggested scheme, the quantum nodes are single atoms confined in high-finesse optical cavities linked by photonic channels. The quantum information written in a superposition of atomic Zeeman states of sending system is faithfully mapped through cavity-assisted Raman scattering onto PNSS of linearly polarized cavity photons. The photons travel to the receiving cavity, where they are coherently absorbed with unit probability creating the same superposition state of the second atom, thus ensuring high-fidelity transfer between distant nodes. We develop this approach at first for photonic qubit and show that this superposition state is no less reliably protected against the propagation losses compared to the single-photon polarization states, whereas the limitation associated with the delivery of more than one photon does not affect the process fidelity. Then, by preserving the advantages of qubits, we extend the developed technique to the case of state transfer by photonic qutrit, which evidently possesses more information capacity. This reliable and efficient scheme promises also a successful distribution of entanglement over long distances in quantum networks.

Superfluid-superradiant mixed phase of the interacting degenerate Fermi gas in an optical cavity

We investigate the ground-state properties of an attractively interactingdegenerate Fermi gas coupling with a high-finesse optical cavity. We predicta new mixed phase with both the superfluid and superradiant properties forthe intermediate fermion-fermion interaction and fermion-photon couplingstrengths. Moreover, in this mixed phase a relatively large ratio of thescaled polarization to the dimensionless mean-field gap, which is in contrastto that in the conventional superfluid regime can be obtained. We alsofigure out rich phase diagrams depending crucially on the atomic resonantfrequency (effective Zeeman field) and address briefly the experimentaldetection of our predicted quantum phases.

A Molecularly Modulated Mode-Locked Laser

A mode-locked laser operating at a frequency over 10 THz is reported, which is three orders of magnitude greater than a standard mode-locked laser. The system used molecules with a Raman gain as an amplifier, while coherent molecular motions were used for optical modulation. Molecules in a high-finesse optical cavity modulated a continuous-wave beam to produce a train of ultrashort optical pulses at a repetition rate corresponding to the frequency of molecular motion. Phase-locking was achieved by an appropriate compensation of the total dispersion of the optical cavity. Thus, the oscillating multiple longitudinal modes were all coupled under phase-matching conditions of parametric four-wave mixing.

Dual-laser frequency-stabilized cavity ring-down spectroscopy for water vapor density measurements

Absolute measurements of water vapor densities have been carried out using a new concept of frequency-stabilized cavity ring-down spectroscopy. Our scheme is based on the use of a pair of phase-locked extended cavity diode lasers, emitting at 1.39 m, one of them being locked to a self-referenced optical frequency comb synthesizer. An intrinsically stable high-finesse optical cavity that tracks the laser frequency scans has been used. High quality, comb-calibrated, absorption spectra have been recorded in a certified H2O/N2 gas mixture at different gas pressures, in coincidence with the 2 transition of the H2 18O + band. Water vapor mole fractions have been determined with a statistical uncertainty of 0.6. Systematic deviations have been identified and carefully quantified, thus leading to an overall uncertainty of 0.8.

Reduction of absorption losses in MOVPE-grown AlGaAs Bragg mirrors.

Residual p-type doping from carbon has been identified as the root cause of excess absorption losses in (Al)GaAs/AlGaAs Bragg mirrors for high-finesse optical cavities when grown by metalorganic vapor phase epitaxy (MOVPE). Through optimization of the growth parameters with the aim of realizing low carbon uptake, we have shown a path for decreasing the parasitic background absorption in these mirrors from 100 to the 10ppm range near 1064nm. This significant reduction is realized via compensation of the carbon acceptors by intentional doping with the donor silicon in the uppermost layer pairs of 40-period GaAs/AlGaAs Bragg mirrors. Thus, we find that such compensation enables MOVPE-derived multilayer mirrors with the potential for a high cavity finesse (>100,000 in the near infrared) approaching the performance levels found with Bragg mirrors grown by molecular beam epitaxy (MBE).