Microwave coupled Zeeman splitting spectroscopy of a cesium nPJ Rydberg atom.

We perform measurements of microwave spectra of cesium Rydberg 51S1/2 → 51PJ transitions with the linewidth approaching the Fourier limit. A two-photon scheme excites the ground-state atoms to the Rydberg 51S1/2 state, and a weak microwave photon couples the Rydberg transition of 51S1/2 → 51PJ. The hyperfine structure of 51P1/2 can be clearly resolved with a narrow linewidth microwave spectra by using the method of ion detection. Furthermore, we investigate the Zeeman effect of the 51P1/2,3/2 state. The theoretical calculations reproduce the measurement well. Our experimental measurements provide a reliable technical solution for the investigation of high angular momentum Rydberg states, which is conducive to further realizing the coherent manipulation of Rydberg energy levels and improving the sensitivity of electromagnetic field measurement.

Dissociation of ultracold cesium Rydberg-ground molecules.

We report the experimental measurements of the decay rate of polar cesium nD5/2 - 6S1/2 Rydberg-ground molecules with a large principal quantum number range of 35 ≤ n ≤ 40. Rydberg molecules are prepared employing the method of two-photon photoassociation and the molecular (atomic) ions, due to autoionization (blackbody photoionization), are detected with a microchannel plate detector. The decay rate Γ of the vibrational ground state of the deep and shadow bound molecules for triplet (TΣ) and mixed singlet-triplet (S,TΣ) are measured by fitting the molecular population with the exponential function. Comparing with the parent atom, the decay rate of the polar Rydberg-ground molecule shows an obvious increase with a magnitude of a few µs. The possible dissociation mechanism of polar Rydberg-ground molecules including a collisional decay, blackbody induced decay, and coupling of adjacent Rydberg states and tunneling decay are discussed in detail. The theoretical model is induced to simulate the measurements, showing agreement.

Robust Ramsey interferometer based on a single Rydberg polariton.

We demonstrate a robust single-photon Ramsey interferometer based on a single Rydberg excitation, where the photon is stored as a Rydberg polariton in an ensemble of atoms. This coherent conversion of the photon to Rydberg polariton enables to split an incoming photon into a superposition state of two Rydberg states by applying microwave fields, which constructs two paths of interferometer. Ramsey interference fringes are demonstrated when we scan either the detuning of the microwave or the free evolution time, from which we can obtain the resonant transition frequency of two Rydberg states. We use the Ramsey-like sequence to demonstrate coherent manipulation of the stored single-photon to construct different interference patterns. In addition, the robustness of the Ramsey interferometer to the fluctuation of incoming photon numbers and optical depth (OD) of the atomic ensemble is tested, showing that the coherent of Ramsey interferometer is preserved for input photon number in a range of Rin < 15 and for OD varying from 1.0 to 4.0. The robust interferometer will find its applications in quantum precision measurement.

Manipulation of single stored-photon with microwave field based on Rydberg polariton.

We demonstrate a coherent microwave manipulation of a single optical photon based on a single Rydberg excitation in an atomic ensemble. Due to the strong nonlinearities in a Rydberg blockade region, a single photon can be stored in the formation of Rydberg polariton using electromagnetically induced transparency (EIT). The manipulation of the stored single photon is performed by applying a microwave field that resonantly couples the nS1/2 and nP3/2, while the coherent readout is performed by mapping the excitation into a single photon. We achieve a single photon source with g(2)(0) = 0.29 ± 0.08 at 80S1/2 without applying microwave fields. By implementing the microwave field during the storage time and retrieval process, we show the Rabi oscillation and modulation of stored photons that can be controlled to retrieve early or late. Rapid modulation frequencies up to 50 MHz can be obtained. Our experimental observations can be well explained via numerical simulations based on an improved superatom model accounting for the dipole-dipole interactions in a Rydberg EIT medium. Our work provides a way to manipulate the stored photons by employing the microwave field, which is significant for developing quantum technologies.

Dephasing of ultracold cesium 80D5/2-Rydberg electromagnetically induced transparency.

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80D5/2 state in a strong interaction regime employing a cesium ultracold cloud. In our experiment, a strong coupling laser couples 6P3/2 to 80D5/2 transition, while a weak probe, driving 6S1/2 to 6P3/2 transition, probes the coupling induced EIT signal. At the two-photon resonance, we observe that the EIT transmission decreases slowly with time, which is a signature of interaction induced metastability. The dephasing rate γOD is extracted with optical depth OD = γODt. We find that the optical depth linearly increases with time at onset for a fixed probe incident photon number Rin before saturation. The dephasing rate shows a nonlinear dependence on Rin. The dephasing mechanism is mainly attributed to the strong dipole-dipole interactions, which leads to state transfer from nD5/2 to other Rydberg states. We demonstrate that the typical transfer time τ0(80D) obtained by the state selective field ionization technique is comparable with the decay time of EIT transmission τ0(EIT). The presented experiment provides a useful tool for investigating the strong nonlinear optical effects and metastable state in Rydberg many-body systems.

Autler-Townes splitting of three-photon excitation of cesium cold Rydberg gases.

We demonstrate the three-photon Autler-Townes (AT) spectroscopy in a cold cesium Rydberg four-level atom by detecting the field ionized Rydberg population. The ground state |6S1/2〉, two intermediate states |6P3/2〉 and |7S1/2〉 and Rydberg state |60P3/2〉 form a cascade four-level atomic system. The three-photon AT spectra and AT splittings are characterized by the Rabi frequency Ω852 and Ω1470 and detuning δ852 of the coupling lasers. Due to the interaction of two coupling lasers with the atoms, the AT spectrum has three peaks denoted with the letters A, B and C. Positions of the peaks and relative AT splittings, γAB and γBC, strongly depend on two coupling lasers. The dependence of the AT splitting, γAB and γBC, on the coupling laser detuning, δ852, and Rabi frequency, Ω852 and Ω1470 are investigated. It is found that the AT splitting γAB mainly comes from the first photon coupling, whereas the γBC mainly comes from the second photon coupling with the atom. The three-photon AT spectra and relevant AT splittings are simulated with the four-level density matrix equation and show good agreement with the theoretical simulations considering the spectral line broadening. Our work is of great significance both for further understanding the interaction between the laser and the atom, and for the application of the Rydberg atom based field measurement.

Rydberg atom-based AM receiver with a weak continuous frequency carrier.

We demonstrate an atom-based amplitude-modulation (AM) receiver for digital communication with a weak continuous frequency carrier using a Rydberg AC Stark effect in a vapor cell and achieve the operating carrier frequency continuously from 0.1 GHz to 5 GHz at a single Rydberg state. A strong local oscillator (LO) field ELO acts as a gain to shift the Rydberg level to a high sensitivity region, and a weak carrier field ECarr keeps the same frequency with the LO field. The digital baseband signals are encoded onto the ECarr using the amplitude modulation technique with the different modulation frequency. The response of Rydberg atom to the baseband signal is probed via a Rydberg electromagnetically induced transparency (EIT). The measured instantaneous bandwidth of the system is about 230 kHz. To demonstrate the performance of our system for an actual communication, we consider a color image as an example, the received image displays that the bit error rate (BER) is less than 5% when the maximum data transfer rate is about 238 kbps. Meanwhile, our system shows the weak carrier field of ECarr ≥ 13.52 µV/cm can be used for the practical communication with BER less than 5%. Our works break the limitation that EIT-AT based atomic receivers only operate at the near resonant frequencies of the Rydberg transitions, making this emerging of quantum technology close to the practical application with high sensitivity and broad bandwidth.

Observation of photoassociation spectroscopy of ultralong 37D5/2 + 6S1/2Cs2 Rydberg molecules.

We present an experimental observation of 37D5/2 + 6S1/2Cs2 Rydberg-ground molecules by employing a two-photon photoassociation method. Two distinct Rydberg-ground molecular signals, deep and shallow bound molecules, are observed at the red detuning of atomic line. In theory, the model of scattering interaction between the Rydberg electron and ground-state atom is used to simulate the experiments. Two potential energy curves with energy minimum, deep pure triplet 3Σ and shallow hyperfine-mixed singlet-triplet 1,3Σ potentials, refer to the attained Rydberg-ground molecular signals, respectively. Calculations of the binding energy of triplet 3Σ and mixed 1,3Σv = 0 states are compared with the measurements. The agreement between the calculated and measured values of the binding energy yields zero-energy scattering lengths as T(0) = -19.2a0 and as S(0) = -1.3a0, respectively.