In this video, I present the latest results obtained with our cavity QED setup where an ensemble of cold atoms is trapped in a fiber-based Fabry-Perot cavity, deep in the strong coupling regime. We have observed cavity protected polaritons in the form of two transmissions peaks of the atoms-cavity system, their linewidth being much narrower than the inhomogeneously-broadened atomic frequency distribution. This effect, which was previously observed in solid-state systems, can be reproduced here with tunable experimental parameters and holds great prospects for preserving coherence in large inhomogeneous quantum systems with possible applications to the field of quantum memories.
In this video, I present the latest results obtained with our cavity QED setup where an ensemble of cold atoms is trapped in a fiber-based Fabry-Perot cavity, deep in the strong coupling regime. We have observed cavity protected polaritons in the form of two transmissions peaks of the atoms-cavity system, their linewidth being much narrower than the inhomogeneously-broadened atomic frequency distribution. This effect, which was previously observed in solid-state systems, can be reproduced here with tunable experimental parameters and holds great prospects for preserving coherence in large inhomogeneous quantum systems with possible applications to the field of quantum memories.
Generating and manipulating multiparticle quantum entangled states is an exciting challenge of modern physics. Along this line, we have built a platform where cold rubidium atoms are strongly coupled to a fiber-based microcavity, under a quantum gas microscope. The atoms are trapped in a lattice at 1560nm, which allows strong and homogeneous coupling to the commensurate probe lattice at 780nm. First, we observe a coherent interaction between the cavity and the atoms, in the strong coupling regime, in spite of a large frequency inhomogeneity induced by the trap. It is the first report of such cavity protection effect with less than 200 emitters. We measure the growing coupling of the dark states to the cavity as the disorder takes over the collective coupling. In the protected regime we engineer frequency-modulated polaritons through a modulation of the atomic frequency. Then, we setup optical tweezers in the microcavity to obtain and manipulate several single atoms. The cavity enables fast and non demolition detection of a single atom in a tweezer. We measure the vacuum Rabi splitting of this atom, demonstrating its strong coupling with an effective cooperativity of 30. Finally, we obtain single atoms in a chain of 9 tweezers. This work opens to way to manipulating many individual atoms strongly coupled to the cavity, with applications in multiparameter quantum metrology, using spatially distributed and locally measurable entanglement as a resource, and quantum simulation of a chain of addressable spins with cavity-mediated infinite range interactions.
Summary form only given. Controlling and characterizing entanglement in large quantum systems is an exciting challenge of modern physics, and a necessary milestone to fulfill the promises of the second quantum revolution. Along this line, we have built a platform where ultracold rubidium atoms are strongly coupled to a fiber-based Fabry-Perot cavity under a quantum gas microscope. Here, the cavity is used to create collective interactions between the atoms, while the microscope is meant to allow for single-qubit manipulation and readout. To maximize the overlap between the atomic distribution and the 780nm cavity mode to which they are coupled, we use an intracavity far off-resonance lattice trap at 1560nm in a configuration where the antinodes of the 1560nm standing wave coincide with antinodes of the 780nm standing wave, which is possible because the two wavelength are commensurate. With this device, we have observed vacuum Rabi frequencies on the order of 60MHz, corresponding to a single-atom cooperativity of about 40, deep into the strong coupling regime. In the short term, we aim at obtaining a 1D chain of single atoms strongly and homogeneously coupled to the cavity, with single atom addressing and detection capabilities. We will discuss at the conference future prospects that we plan to address with this platform, such as using cavity-assisted Raman transitions to implement, within a fully controlled experimental system, spin models with photon-mediated interactions [4], or the Dicke Hamiltonian [5] where many-body entanglement is known to occur in the vicinity of the associated quantum phase transition.
We investigate theoretically the coupling of a cavity mode to a continuous distribution of emitters. We discuss the influence of the emitters' inhomogeneous broadening on the existence and on the coherence properties of the polaritonic peaks. We find that their coherence depends crucially on the shape of the distribution and not only on its width. Under certain conditions the coupling to the cavity protects the polaritonic states from inhomogeneous broadening, resulting in a longer storage time for a quantum memory based on emitter ensembles. When two different ensembles of emitters are coupled to the resonator, they support a peculiar collective dark state, which is also very attractive for the storage of quantum information.
We explore the high-density, nonlinear regime of atom-cavity coupling for a gas of three-level atoms at high temperature inside an optical cavity, interacting with the cavity field and a strong driving field. We find a region of parameters where the two side peaks in the transmission spectrum (which, in the linear regime, are associated with ``bright polaritons'') split into two pairs of peaks. Experimental results are presented along with a theoretical model that indicates that this phenomenon is unique to the three-level system in the large Doppler-broadening regime.
Rare-earth ions doped in crystals are renowned for their excellent coherence properties and large inhomogeneous broadening, which make them ideal for quantum interfaces with broadband photons. These properties have made them one of the leading technologies in quantum optical memories and a promising candidate for optical-to-microwave conversion. To take advantage of the full bandwidth of the rare-earth ensemble, one must overcome the decoherence of a broadband collective excitation due to inhomogeneous broadening. To this end, techniques based on controllable rephasing, such as atomic frequency comb (AFC) or controlled reversible inhomogeneous broadening (CRIB) memories, have been developed with great success. Recently, an alternative method was proposed to suppress the decoherence of an inhomogeneous ensemble via strong coupling to a cavity, a phenomenon called cavity protection. This technique has been demonstrated in the microwave domain with an NV spin ensemble, but has not been demonstrated in the optical domain. Here, we demonstrate cavity protection in the optical domain at the single photon level using an ensemble of rare earths ions coupled to a nanophotonic resonator. The reduction in decoherence due to the cavity-protection effect enables transfer of ultrafast (~50 GHz) frequency qubits into the collective ion excitation and retrieval with 98.7% fidelity. Building on these results to transfer these excitations to long-lived spin states would enable broadband, on-demand quantum memories. Furthermore, this works compliments the work done coupling rare-earths to superconducting resonators in the microwave regime with potential for applications in optical-to-microwave transducers.
The interaction of laser cooled atoms with resonant light is determined by the natural linewidth of the excited state. An optical cavity is another optically resonant system where the loss from the cavity determines the resonant optical response of the system. The near resonant combination of an optical Fabry-Pérot cavity with laser cooled and trapped atoms couples two distinct optical resonators via light and has great potential for precision measurements and the creation of versatile quantum optics systems. Here we show how driven magneto-optically trapped atoms in collective strong coupling regime with the cavity leads to lasing at a frequency red detuned from the atomic transition. Lasing is demonstrated experimentally by the observation of a lasing threshold accompanied by polarization and spatial mode purity, and line-narrowing in the outcoupled light. Spontaneous emission into the cavity mode by the driven atoms stimulates lasing action, which is capable of operating as a continuous wave laser in steady state, without a seed laser. The system is modeled theoretically, and qualitative agreement with experimentally observed lasing is seen. Our result opens up a range of new measurement possibilities with this system.