arXiv subjects

Susanne F. Yelin

Publications and source records attributed to Susanne F. Yelin.

118 records · Page 7Linked to original sources

arXiv2013

Enhanced index of refraction in four-wave mixing media

Refractive index enhancement accompanied by vanishing absorption in a four-level atomic system interacting with two control and two probe fields in a regime of four-wave mixing (FWM) has been predicted and studied in the present work. We analyzed the maximal index enhancement in the four-level FWM system and gave index estimates for a real atomic gas of $^{40}$K, taking into account its multilevel structure and collisional and Doppler broadenings at large atomic densities. We also discussed how vanishing absorption with no nearby amplification can be realized in a two species system, consisting of a four-level FWM and a two-level system, where the latter provides additional absorption for one of the probe fields. We numerically estimated the index change in a system composed of $^{40}$K and $^{39}$K gases.

quant-ph↗

arXiv2013

Vibrational spectroscopy of polar molecules with superradiance

We investigate cooperative phenomena and superradiance for vibrational transitions in polar molecule spectroscopy when a high optical-depth (OD) sample is studied. Such cooperativity comes from the build-up of inter-particle coherence through dipole-dipole interactions and leads to the speed-up of decay process. We compare our calculation to recent work [Deiglmayr et al., Eur. Phys. J. D 65, 99 (2011)] and find very good agreement, suggesting that superradiant effects need to be included in a wide variety of ultracold molecule setups including vibrational and rotational states.

physics.atom-ph↗

arXiv2013

Single atom trapping and control inside a nanosize photonic crystal cavity

We analyze a possibility to trap, control and load a single atom inside a nanosize cavity formed in a photonic crystal. We consider a 1D nanobeam crystal having two nearly degenerate localized modes with mode maxima at the central air gap, forming a cavity with a mode volume <λ^{3}. For this system we found that an atom can be trapped by a mode detuned from an atomic transition and controled by the second resonant mode. We show that atomic motion can be cooled using cavity-enhanced rf Sisyphus cooling. We also discuss how an atom can be loaded inside the nanosize crystal air gap from short-wavelength optical tweezers.

quant-ph↗

arXiv2012

Dissipative Phase Transition in Central Spin Systems

We investigate dissipative phase transitions in an open central spin system. In our model the central spin interacts coherently with the surrounding many-particle spin environment and is subject to coherent driving and dissipation. We develop analytical tools based on a self-consistent Holstein-Primakoff approximation that enable us to determine the complete phase diagram associated with the steady states of this system. It includes first and second-order phase transitions, as well as regions of bistability, spin squeezing and altered spin pumping dynamics. Prospects of observing these phenomena in systems such as electron spins in quantum dots or NV centers coupled to lattice nuclear spins are briefly discussed.

quant-ph↗

arXiv2011

Rydberg atom mediated polar molecule interactions: a tool for molecular-state conditional quantum gates and individual addressability

We study the possibility to use interaction between a polar molecule in the ground electronic and vibrational state and a Rydberg atom to construct two-qubit gates between molecular qubits and to coherently control molecular states. A polar molecule within the electron orbit in a Rydberg atom can either shift the Rydberg state, or form Rydberg molecule. Both the atomic shift and the Rydberg molecule states depend on the initial internal state of the polar molecule, resulting in molecular state dependent van der Waals or dipole-dipole interaction between Rydberg atoms. Rydberg atoms mediated interaction between polar molecules can be enhanced up to $10^{3}$ times. We describe how the coupling between a polar molecule and a Rydberg atom can be applied to coherent control of molecular states, specifically, to individual addressing of molecules in an optical lattice and non-destructive readout of molecular qubits.

quant-ph↗

arXiv2009

Phase gate and readout with an atom/molecule hybrid platform

We suggest a combined atomic/molecular system for quantum computation, which takes advantage of highly developed techniques to control atoms and recent experimental progress in manipulation of ultracold molecules. We show that two atoms of different species in a given site, {\it e.g.}, in an optical lattice, could be used for qubit encoding, initialization and readout, with one atom carrying the qubit, the other enabling a gate. In particular, we describe how a two-qubit phase gate can be realized by transferring a pair of atoms into the ground rovibrational state of a polar molecule with a large dipole moment, and allowing two molecules to interact via their dipole-dipole interaction. We also discuss how the reverse process of coherently transferring a molecule into a pair of atoms could be used as a readout tool for molecular quantum computers.

quant-ph↗

arXiv2009

Low-loss negative refraction by laser induced magneto-electric cross-coupling

We discuss the feasibility of negative refraction with reduced absorption in coherently driven atomic media. Coherent coupling of an electric and a magnetic dipole transition by laser fields induces magneto-electric cross-coupling and negative refraction at dipole densities which are considerably smaller than necessary to achieve a negative permeability. At the same time the absorption gets minimized due to destructive quantum interference and the ratio of negative refraction index to absorption becomes orders of magnitude larger than in systems without coherent cross-coupling. The proposed scheme allows for a fine-tuning of the refractive index. We derive a generalized expression for the impedance of a medium with magneto-electric cross coupling and show that impedance matching to vacuum can easily be achieved. Finally we discuss the tensorial properties of the medium response and derive expressions for the dependence of the refractive index on the propagation direction.

quant-ph↗

arXiv2008

Efficient formation of ground state ultracold molecules via STIRAP from the continuum at a Feshbach resonance

We develop a complete theoretical description of photoassociative Stimulated Raman Adiabatic Passage (STIRAP) near a Feshbach resonance in a thermal atomic gas. We show that it is possible to use low intensity laser pulses to directly excite the continuum at a Feshbach resonance and transfer nearly the entire atomic population to the lowest rovibrational level in the molecular ground state. In case of a broad resonance, commonly found in several diatomic alkali molecules, our model predicts a transfer efficiency $η$ up to 97% for a given atom pair, and up to 70% when averaged over an atomic ensemble. The laser intensities and pulse durations needed for optimal transfer are $10^2-10^3$ W/cm$^2$ and several $μ$s. Such efficiency compares to or surpasses currently available techniques for creating stable diatomic molecules, and the versatility of this approach simplifies its potential use for many molecular species.

quant-ph↗

arXiv2007

Tunable negative refraction without absorption via electromagnetically induced chirality

We show that negative refraction with minimal absorption can be obtained by means of quantum interference effects similar to electromagnetically induced transparency. Coupling a magnetic dipole transition coherently with an electric dipole transition leads to electromagnetically induced chirality, which can provide negative refraction without requiring negative permeability, and also suppresses absorption. This technique allows negative refraction in the optical regime at densities where the magnetic susceptibility is still small and with refraction/absorption ratios that are orders of magnitude larger than those achievable previously. Furthermore, the value of the refractive index can be fine-tuned via external laser fields, which is essential for practical realization of sub-diffraction-limit imaging.

quant-ph↗

arXiv1998

Radiative atom-atom interactions in optically dense media: Quantum corrections to the Lorentz-Lorenz formula

Generalized single-atom Maxwell-Bloch equations for optically dense media are derived taking into account non-cooperative radiative atom-atom interactions. Applying a Gaussian approximation and formally eliminating the degrees of freedom of the quantized radiation field and of all but a probe atom leads to an effective time-evolution operator for the probe atom. The mean coherent amplitude of the local field seen by the atom is shown to be given by the classical Lorentz-Lorenz relation. The second-order correlations of the field lead to terms that describe relaxation or pump processes and level shifts due to multiple scattering or reabsorption of spontaneously emitted photons. In the Markov limit a nonlinear and nonlocal single-atom density matrix equation is derived. To illustrate the effects of the quantum corrections we discuss amplified spontaneous emission and radiation trapping in a dense ensemble of initially inverted two-level atoms and the effects of radiative interactions on intrinsic optical bistability in coherently driven systems.

quant-ph↗