Raman Transitions Research Articles

Efficient Preparation of D2 Molecules in v=2 by Stimulated Raman Pumping

We report the preparation of D2 molecules in v=2 level in molecular beam condition. A single longitudinal mode laser system was used for excitation of D2 from (v=0, j=0) to (v=2, j=0) with the scheme of stimulated Raman pumping. An excitation efficiency of 25.2% has been achieved, which was determined by the scheme of resonance-enhanced multiphoton ionization. Dependence of relative excitation efficiency on laser energy has been measured. We found that the increasing rate of excitation efficiency became slower as pulse energy of Stokes laser increase, while the excitation efficiency still increases approximately linearly with pump pulse energies up to 60 mJ. The spectral line shapes of Raman transition was also measured at different laser energies and considerable dynamical Stark effect was observed. A single peak was found on the three dimension surface of relative excitation efficiency, indicating the process occurred in the present study is a process of stimulated Raman pumping instead of stimulated adiabatic Raman passage.

Multiaxis atom interferometry with a single-diode laser and a pyramidal magneto-optical trap

Atom interferometry has become one of the most powerful technologies for precision measurements. To develop simple, precise, and versatile atom interferometers for inertial sensing, we demonstrate an atom interferometer measuring acceleration, rotation, and inclination by pointing Raman beams toward individual faces of a pyramidal mirror. Only a single diode laser is used for all functions, including atom trapping, interferometry, and detection. Efficient Doppler-sensitive Raman transitions are achieved without the velocity selecting the atom sample, and with zero differential AC Stark shift between the cesium hyperfine ground states, increasing signal-to-noise and suppressing systematic effects. We measure gravity along two axes (vertical and 45$^\circ$ to the vertical), rotation, and inclination with sensitivities of 6$\,\mu$m/s$^2/\sqrt{\rm Hz}$, 300$\,\mu$rad/s/$\sqrt{\rm Hz}$, and 4$\,\mu$rad/$\sqrt{\rm Hz}$, respectively. This work paves the way toward deployable multiaxis atom interferometers for geodesy, geology, or inertial navigation.

Dissipation induced asymmetric steering of distant atomic ensembles

The asymmetric steering effects of separated atomic ensembles denoted by the effective bosonic modes have been explored by the means of quantum reservoir engineering in the setting of the cascaded cavities, in each of which an atomic ensemble is involved. It is shown that the steady-state asymmetric steering of the mesoscopic objects is unconditionally achieved via the dissipation of the cavities, by which the nonlocal interaction occurs between two atomic ensembles, and the direction of steering could be easily controlled through variation of certain tunable system parameters. One advantage of the present scheme is that it could be rather robust against parameter fluctuations, and does not require the accurate control of evolution time and the original state of the system. Furthermore, the double-channel Raman transitions between the long-lived atomic ground states are used and the atomic ensembles act as the quantum network nodes, which makes our scheme insensitive to the collective spontaneous emission of atoms.

Multidimensional Spectral Fingerprints of a New Family of Coherent Analytical Spectroscopies.

Triply resonant sum frequency (TRSF) and doubly vibrationally enhanced (DOVE) spectroscopies are examples of a recently developed family of coherent multidimensional spectroscopies (CMDS) that are analogous to multidimensional NMR and current analytical spectroscopies. CMDS methods are particularly promising for analytical applications because their inherent selectivity makes them applicable to complex samples. Like NMR, they are based on creating quantum mechanical superposition states that are fully coherent and lack intermediate quantum state populations that cause quenching or other relaxation effects. Instead of the nuclear spin states of NMR, their multidimensional spectral fingerprints result from creating quantum mechanical mixtures of vibrational and electronic states. Vibrational states provide spectral selectivity, and electronic states provide large signal enhancements. This paper presents the first electronically resonant DOVE spectra and demonstrates the capabilities for analytical chemistry applications by comparing electronically resonant TRSF and DOVE spectra with each other and with infrared absorption and resonance Raman spectra using a Styryl 9 M dye as a model system. The methods each use two infrared absorption transitions and a resonant Raman transition to create a coherent output beam, but they differ in how they access the vibrational and electronic states and the frequency of their output signal. Just as FTIR, UV-vis, Raman, and resonance Raman are complementary methods, TRSF and DOVE methods are complementary to coherent Raman methods such as coherent anti-Stokes Raman spectroscopy (CARS).

Cavity QED Engineering of Spin Dynamics and Squeezing in a Spinor Gas.

We propose a method for engineering spin dynamics in ensembles of integer-spin atoms confined within a high-finesse optical cavity. Our proposal uses cavity-assisted Raman transitions to engineer a Dicke model for integer-spin atoms, which, in a dispersive limit, reduces to effective atom-atom interactions within the ensemble. This scheme offers a promising and flexible new avenue for the exploration of a wide range of spinor many-body physics. As an example of this, we present results showing that this method can be used to generate spin-nematic squeezing in an ensemble of spin-1 atoms. With realistic parameters, the scheme should enable substantial squeezing on time scales much shorter than current experiments with spin-1 Bose-Einstein condensates.

Matterwave interferometric velocimetry of cold Rb atoms

We consider the matterwave interferometric measurement of atomic velocities, which forms a building block for all matterwave inertial measurements. A theoretical analysis, addressing both the laboratory and atomic frames and accounting for residual Doppler sensitivity in the beamsplitter and recombiner pulses, is followed by an experimental demonstration, with measurements of the velocity distribution within a 20 K cloud of rubidium atoms. Our experiments use Raman transitions between the long-lived ground hyperfine states, and allow quadrature measurements that yield the full complex interferometer signal and hence discriminate between positive and negative velocities. The technique is most suitable for measurement of colder samples.

Coherently induced grating in refractive index enhanced medium**Project supported by the National Natural Science Foundation of China (Grant Nos. 11204367 and 61475191) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. GK201503022 and GK201601008).

We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields. As a result of interaction between the absorptive and amplified Raman resonances, the refractive index of the medium can be enhanced and modulated periodically. Then a sinusoidal grating, which can diffract the probe field into high-order directions, is coherently formed in the medium. The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium. The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields. The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.

Squeezing giant spin states via geometric phase control in cavity-assisted Raman transitions

Squeezing ensemble of spins provides a way to surpass the standard quantum limit in quantum metrology and test the fundamental physics as well, and therefore attracts broad interest. Here we propose an experimentally accessible protocol to squeeze a giant ensemble of spins via the geometric phase control (GPC). Using the cavity-assisted Raman transition (CART) in a double Λ-type system, we realize an effective Dicke model. Under the condition of vanishing effective spin transition frequency, we find a particular evolution time where the cavity decouples from the spins and the spin ensemble is squeezed considerably. Our scheme combines the CART and the GPC, and has the potential to improve the sensitivity in quantum metrology with spins by about two orders.

Mølmer–Sørensen entangling gate for cavity QED systems

The Mølmer–Sørensen gate is a state-of-the-art entangling gate in ion trap quantum computing where the gate fidelity can exceed 99%. Here we propose an analogous implementation in the setting of cavity QED. The cavity photon mode acts as the bosonic degree of freedom in the gate in contrast to that played by the phonon mode in ion traps. This is made possible by utilising cavity assisted Raman transitions interconnecting the logical qubit states embedded in a four-level energy structure, making the ‘anti-Jaynes–Cummings’ term available under the rotating-wave approximation. We identify practical sources of infidelity and discuss their effects on the gate performance. Our proposal not only demonstrates an alternative entangling gate scheme but also sheds new light on the relationship between ion traps and cavity QED, in the sense that many techniques developed in the former are transferable to the latter through our framework.

Spectral properties of single photons from quantum emitters

Quantum networks require flying qubits that transfer information between the nodes. This may be implemented by means of single atoms (the nodes) that emit and absorb single photons (the flying qubits) and requires full control of photon absorption and emission by the individual emitters. In this work, we theoretically characterize the wave packet of a photon emitted by a single atom undergoing a spontaneous Raman transition in a three-level scheme. We investigate several excitation schemes that are experimentally relevant and discuss control parameters that allow one to tailor the spectrum of the emitted photon wave packet.

Entanglement Property of Bose-Einstein Condensate Atoms and the Photons of the Probe Light Field Via Stimulated Raman Transition

We investigated the entanglement property of Bose-Einstein condensate atoms and the photons of the probe light field via stimulated Raman transition. By numerical calculation, we see that the entanglement can be generated by adjusting the frequency of the probe light field, the light-atom dipole interaction strength, the energies of two modes, the interatomic interaction strength and the evolution time.

Stimulated Raman transitions from the metastable 2s state of hydrogen

We consider the hydrogen atom H() exposed to a short laser pulse with a central frequency ranging from 136 eV to 1.5 keV ( au) at the intensity of W cm−2. We study stimulated Raman scattering transitions to the ground state (anti-Stokes) and to the upper ns, np and nd states (with ) (Stokes). Nondipole (retardation) effects are included up to (c is the speed of light in a vacuum). The calculation of the transition probabilities, based on the integration of the time-dependent Schrödinger equation, is confronted with results obtained by applying perturbation theory. The two methods are in very good agreement. We show that retardation effects play an important role for frequencies larger than a few hundred eV and pulse durations of the order of the femtosecond. In this regime, as the frequency increases, the contribution of the term dominates over (where and denote the vector potential of the field and the momentum operator, respectively). Results are presented for various values of the pulse frequency and duration.

Time-Resolved Vibrational Spectroscopy of Polytetrafluoroethylene Under Laser-Shock Compression.

Shock-wave-induced high pressure and nanosecond time-resolved Raman spectroscopic experiments were performed to examine the dynamic response of polytetrafluoroethylene (PTFE) in confinement geometry targets. Time-resolved Raman spectroscopy was used to observe the pressure-induced molecular and chemical changes on nanosecond time scale. Raman spectra were measured as a function of shock pressure in the 1.2-2.4 GPa range. Furthermore, the symmetric stretching mode at 729 cm-1 of CF2 was compared to corresponding static high-pressure measurements carried out in a diamond anvil cell, to see if any general trend can be established. The symmetric stretching mode of CF2 at 729 cm-1 is the most intense Raman transition in PTFE and is very sensitive to change in pressure. Therefore, it can also be utilized as a pressure gauge for large amplitude shock wave compression experiments. A maximum blueshift of 12 cm-1 for the 729 cm-1 vibrational mode has been observed for the present experimental pressure range. A comparative study on the similarities and differences from the earlier work has been done in detail. One-dimensional radiation hydrodynamic simulations were performed to validate our shock compression results and are in very good agreement.

Ground-state blockade of Rydberg atoms and application in entanglement generation

We propose a mechanism of ground-state blockade between two $N$-type Rydberg atoms in virtue of Rydberg-antiblockade effect and Raman transition. Inspired by the quantum Zeno effect, the strong Rydberg antiblockade interaction plays a role in frequently measuring one ground state of two, leading to a blockade effect for double occupation of the corresponding quantum state. By encoding the logic qubits into the ground states, we efficiently avoid the spontaneous emission of the excited Rydberg state, and maintain the nonlinear Rydberg-Rydberg interaction at the same time. As applications, we discuss in detail the feasibility of preparing two-atom and three-atom entanglement with ground-state blockade in closed system and open system, respectively, which shows that a high fidelity of entangled state can be obtained with current experimental parameters.

Storage of polarization-entangled THz-bandwidth photons in a diamond quantum memory

Bulk diamond phonons have been shown to be a versatile platform for the generation, storage, and manipulation of high-bandwidth quantum states of light. Here we demonstrate a diamond quantum memory that stores, and releases on demand, an arbitrarily polarized $\sim$250 fs duration photonic qubit. The single-mode nature of the memory is overcome by mapping the two degrees of polarization of the qubit, via Raman transitions, onto two spatially distinct optical phonon modes located in the same diamond crystal. The two modes are coherently recombined upon retrieval and quantum process tomography confirms that the memory faithfully reproduces the input state with average fidelity $0.784\pm0.004$ with a total memory efficiency of $(0.76\pm0.03)\%$. In an additional demonstration, one photon of a polarization-entangled pair is stored in the memory. We report that entanglement persists in the retrieved state for up to 1.3 ps of storage time. These results demonstrate that the diamond phonon platform can be used in concert with polarization qubits, a key requirement for polarization-encoded photonic processing.

Center-of-mass-momentum-dependent interaction between ultracold atoms

We show that a type of two-body interaction, which depends on the momentum of the center of mass (COM) of these two particles, can be realized in ultracold atom gases with a laser-modulated magnetic Feshbach resonance (MFR). Here the MFR is modulated by two laser beams propagating along different directions, which can induce Raman transition between two-body bound states. The Doppler effect causes the two-atom scattering length to be strongly dependent on the COM momentum of these two atoms. As a result, the effective two-atom interaction is COM-momentum dependent, while the one-atom free Hamiltonian is still the simple kinetic energy p^2/(2m).

Tunable Polarons in Bose-Einstein Condensates

A toolbox for the quantum simulation of polarons in ultracold atoms is presented. Motivated by the impressive experimental advances in the area of ultracold atomic mixtures, we theoretically study the problem of ultracold atomic impurities immersed in a Bose-Einstein condensate mixture (BEC). The coupling between impurity and BEC gives rise to the formation of polarons whose mutual interaction can be effectively tuned using an external laser driving a quasi-resonant Raman transition between the BEC components. Our scheme allows one to change the effective interactions between polarons in different sites from attractive to zero. This is achieved by simply changing the intensity and the frequency of the two lasers. Such arrangement opens new avenues for the study of strongly correlated condensed matter models in ultracold gases.

Raman self-induced-transparency soliton trains in hollow-core photonic crystals

Periodic trains of non-topological dark and bright optical solitons are proposed as one of the possible nonlinear optical structures that could be generated during Raman transitions in nonlinear hollow-core photonic crystal fibers filled with gas. It is shown that Stokes-like probe fields, generated by stimulated Raman transitions upon propagation of the master pump in the hollow-core fiber, form a broadband spectrum, whose discrete branch is populated by several distinct localized periodic soliton modes with well-defined “quantum numbers”. Such soliton trains, which are intended to complement recently proposed single-pulse and single-dark solitons for multi-channel communication applications, can be formed by temporal quantum entanglements of the single-soliton fields. Attention is laid on a possibility to generate such soliton trains in the absence of Kerr nonlinearity, and total controllability of their shape profiles including their temporal periods and average widths is demonstrated through variations of characteristic parameters of the hollow-core photonic crystal fiber.

Designing a cavity-mediated quantum cphase gate between NV spin qubits in diamond

While long spin coherence times and efficient single-qubit quantum control have been implemented successfully in nitrogen-vacancy (NV) centers in diamond, the controlled coupling of remote NV spin qubits remains challenging. Here, we propose and analyze a controlled-phase (CPHASE) gate for the spins of two NV centers embedded in a common optical cavity and driven by two off-resonant lasers. In combination with previously demonstrated single-qubit gates, CPHASE allows for arbitrary quantum computations. The coupling of the NV spin to the cavity mode is based upon Raman transitions via the NV excited states and can be controlled with the laser intensities and relative phase. We find characteristic laser frequencies at which the scattering amplitude of a laser photon into the cavity mode is strongly dependent on the NV center spin. A scattered photon can be reabsorbed by another selectively driven NV center and generate a conditional phase (CPHASE) gate. Gate times around 200 ns are within reach, nearly three orders of magnitude shorter than typical NV spin coherence times of around 10 microseconds. The separation between the two interacting NV centers is only limited by the extension of the cavity.

Location-dependent Raman transition in gravity-gradient measurements using dual atom interferometers

The location-dependent Raman transition was investigated based on dual atom interferometers which were designed for gravity-gradient measurements. The cross talk between the Raman beam pairs generated by an electro-optical modulator make the Raman transition location dependent. Therefore, the fringe contrast also depends on the location where the Raman pulses interact with the atoms, so it is important to adjust the interaction location to optimize the precision of the gravity-gradient measurements. To further reduce the residual cross talk, the detuning of the Raman beams for $^{85}\mathrm{Rb}$ atoms was controlled using the saturated absorption spectra of the $^{87}\mathrm{Rb}$ atoms. The optimal location for the Raman transition was determined by theoretical analysis and modulation experiments, and the atomic trajectory was optimized and applied to the gravity-gradient measurements. The resolution of the differential gravity measurement evaluated by the Allan deviation was $4.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ m/${\mathrm{s}}^{2}$ @ 15 000 s, and the corresponding resolution of the gravity gradient measurement was 7.4 E @ 15 000 s.