# Publications by Martin Kiffner

## Three-body bound states in dipole-dipole interacting Rydberg atoms

Physical Review Letters **111** (2013)

We show that the dipole-dipole interaction between three identical Rydberg atoms can give rise to bound trimer states. The microscopic origin of these states is fundamentally different from Efimov physics. Two stable trimer configurations exist where the atoms form the vertices of an equilateral triangle in a plane perpendicular to a static electric field. The triangle edge length typically exceeds R≈2 μm, and each configuration is twofold degenerate due to Kramers degeneracy. The depth of the potential wells and the triangle edge length can be controlled by external parameters. We establish the Borromean nature of the trimer states, analyze the quantum dynamics in the potential wells, and describe methods for their production and detection. © 2013 American Physical Society.

## Abelian and non-Abelian gauge fields in dipole-dipole interacting Rydberg atoms

Journal of Physics B: Atomic, Molecular and Optical Physics **46** (2013)

We show that the dipole-dipole interaction between two Rydberg atoms can lead to substantial Abelian and non-Abelian gauge fields acting on the relative motion of the two atoms. We demonstrate how the gauge fields can be evaluated by numerical techniques. In the case of adiabatic motion in a single internal state, we show that the gauge fields give rise to a magnetic field that results in a Zeeman splitting of the rotational states. In particular, the ground state of a molecular potential well is given by the first excited rotational state. We find that our system realizes a synthetic spin-orbit coupling where the relative atomic motion couples to two internal two-atom states. The associated gauge fields are non-Abelian. © 2013 IOP Publishing Ltd.

## Magnetic monopoles and synthetic spin-orbit coupling in Rydberg macrodimers.

Phys Rev Lett **110** (2013) 170402-

We show that sizable Abelian and non-Abelian gauge fields arise in the relative motion of two dipole-dipole interacting Rydberg atoms. Our system exhibits two magnetic monopoles for adiabatic motion in one internal two-atom state. These monopoles occur at a characteristic distance between the atoms that is of the order of one micron. The deflection of the relative motion due to the Lorentz force gives rise to a clear signature of the effective magnetic field. In addition, we consider nonadiabatic transitions between two near-degenerate internal states and show that the associated gauge fields are non-Abelian. We present quantum mechanical calculations of this synthetic spin-orbit coupling and show that it realizes a velocity-dependent beam splitter.

## Dipole-dipole-coupled double-Rydberg molecules

Physical Review A - Atomic, Molecular, and Optical Physics **86** (2012)

We show that the dipole-dipole interaction between two Rydberg atoms can give rise to long-range molecules. The binding potential arises from two states that converge to different separated-atom asymptotes. These states interact weakly at large distances, but start to repel each other strongly as the van der Waals interaction turns into a resonant dipole-dipole interaction with decreasing separation between the atoms. This mechanism leads to the formation of an attractive well for one of the potentials. If the two separated-atom asymptotes come from the small Stark splitting of an atomic Rydberg level, which lifts the Zeeman degeneracy, the depth of the well and the location of its minimum are controlled by the external electric field. We discuss two different geometries that result in a localized and a donut-shaped potential, respectively. © 2012 American Physical Society.

## Steady-state negative Wigner functions of nonlinear nanomechanical oscillators

New Journal of Physics **14** (2012)

We propose a scheme for preparing nanomechanical oscillators in nonclassical steady states, characterized by a pronounced negative Wigner function. In our optomechanical approach, the mechanical oscillator couples to multiple laser-driven resonances of an optical cavity. By lowering the resonance frequency of the oscillator via an inhomogeneous electrostatic field, we significantly enhance its intrinsic geometric nonlinearity per phonon. This causes the motional sidebands to split into separate spectral lines for each phonon number and transitions between individual phonon Fock states can be selectively addressed. We show that this enables the preparation of the nanomechanical oscillator in a single-phonon Fock state. Our scheme can, for example, be implemented with a carbon nanotube dispersively coupled to the evanescent field of a state of the art whispering gallery mode microcavity. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

## Dissipative quantum-light-field engineering

PHYSICAL REVIEW A **85** (2012) ARTN 023812

## Cavity optomechanics with nonlinear mechanical resonators in the quantum regime

Optics InfoBase Conference Papers (2011)

## Cavity optomechanics with nonlinear mechanical resonators in the quantum regime

2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011 (2011)

The coupling of light and a mechanical resonator within an optomechanical setup can have significant effects on both the light field inside the cavity and the motion of the mechanical resonator. A prominent example is the cavity assisted side-band cooling of the mechanical motion, leading to low phonon occupation and thereby approaching the quantum regime [1,2]. However, while the preparation of highly nonclassical light fields like single photon states, entangled states or Schrdinger cat states is today an inherent part of the quantum optics toolbox, the preparation of nonclassical states for nanomechanical devices still constitutes a major challenge [3]. Since the dynamics of purely harmonic oscillators will, even in the quantum regime, not differ from its classical analogue, a crucial requirement for observing quantum effects are effective nonlinearities which are typically provided by an ancilla system (ideally a qubit). Here we explore the alternative paradigm of exploiting the geometric nonlinearity inherent to doubly-clamped mechanical resonators. Thus, we consider the physics of a nanomechanical resonator with a Duffing nonlinearity of the form X4, coupled to different cavity modes that are each driven by a detuned laser. Here X denotes the mechanical displacement and the strength of the nonlinearity. The system is coupled to its environment with decay rates kj for the cavity modes and m for the mechanical mode. © 2011 IEEE.

## Dissipation-induced correlations in one-dimensional bosonic systems

New Journal of Physics **13** (2011)

The quantum dynamics of interacting bosons in a one-dimensional (1D) system is investigated numerically. We consider dissipative and conservative two-particle interactions, and integrate the master equation describing the system dynamics via a time-evolving block-decimation (TEBD) algorithm. Our numerical simulations directly apply to stationary-light polaritons in systems where atoms and photons are confined to the hollow core of a photonic crystal fibre. We show that a two-particle loss term can drive an initially uncorrelated state into a regime where correlations effectively inhibit the dissipation of particles. The correlations induced by two-particle losses are compared with those generated by an elastic repulsion. For the considered time range, we find a similar behaviour in local density-density correlations but we find differences in non-local correlations. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

## Subwavelength optical lattices induced by position-dependent dark states

Physical Review A - Atomic, Molecular, and Optical Physics **83** (2011)

A method for the generation of subwavelength optical lattices based on multilevel dark states is proposed. The dark state is formed by a suitable combination of standing wave light fields, leading to position-dependent populations of the ground states. An additional field coupling dispersively to one of the ground states translates this position dependence into a subwavelength optical potential. We provide two semiclassical approaches to understand the involved physics, and demonstrate that they lead to identical results in a certain meaningful limit. Then we apply a Monte Carlo simulation technique to study the full quantum dynamics of the subwavelength trapping. Finally, we discuss the relevant time scales for the trapping, optimum conditions, and possible implementations. © 2011 American Physical Society.

## Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave

Nature Physics **7** (2011) 379-382

In spontaneous emission an atom in an excited state undergoes a transition to the ground state and emits a single photon. Associated with the emission is a change of the atomic momentum due to photon recoil. Photon emission can be modified close to surfaces and in cavities. For an ion, localized in front of a mirror, coherence of the emitted resonance fluorescence has been reported. Previous experiments demonstrated that spontaneous emission destroys motional coherence. Here we report on motional coherence created by a single spontaneous emission event close to a mirror surface. The coherence in the free atomic motion is verified by atom interferometry. The photon can be regarded as a beamsplitter for an atomic matter-wave and consequently our experiment extends the original recoiling slit Gedanken experiment by Einstein to the case where the slit is in a robust coherent superposition of the two recoils associated with the two paths of the quanta.

## Vacuum-induced processes in multilevel atoms

Progress in Optics **55** (2010) 85-197

## Master equation approach for interacting slow- and stationary-light polaritons

Physical Review A - Atomic, Molecular, and Optical Physics **82** (2010)

A master equation approach for the description of dark-state polaritons in coherently driven atomic media is presented. This technique provides a description of light-matter interactions under conditions of electromagnetically induced transparency (EIT) that is well suited for the treatment of polariton losses. The master equation approach allows us to describe general polariton-polariton interactions that may be conservative, dissipative, or a mixture of both. In particular, it enables us to study dissipation-induced correlations as a means for the creation of strongly correlated polariton systems. Our technique reveals a loss mechanism for stationary-light polaritons that has not been discussed so far. We find that polariton losses in level configurations with nondegenerate ground states can be a multiple of those in level schemes with degenerate ground states. © 2010 The American Physical Society.

## Dissipation-induced Tonks-Girardeau gas of polaritons

Physical Review A - Atomic, Molecular, and Optical Physics **81** (2010)

A scheme for the generation of a Tonks-Girardeau (TG) gas of polaritons with purely dissipative interaction is described. We put forward a master equation approach for the description of stationary light in atomic four-level media and show that, under suitable conditions, two-particle decays are the dominant photon loss mechanism. These dissipative two-photon losses increase the interaction strength by at least one order of magnitude as compared to dispersive two-photon processes and can drive the polaritons into the TG regime. Characteristic correlations of the TG gas, including quantities that distinguish it from free fermions, can be measured via standard quantum optical techniques. Our scheme thus allows one to feasibly generate highly correlated photon states, which can be of considerable use in quantum-information processing and precision measurements. © 2010 The American Physical Society.

## Resonant interferometric lithography beyond the diffraction limit.

Phys Rev Lett **100** (2008) 073602-

A novel approach for the generation of subwavelength structures in interferometric optical lithography is described. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. Since this process only comprises resonant atom-field interactions, a multiphoton absorption medium is not required. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at very low laser intensities.

## Probing quantum superposition states with few-cycle laser pulses

Journal of the Optical Society of America B: Optical Physics **26** (2009) 1912-1917

The quantum dynamics of a two-level system illuminated by a few-cycle pulse with an adjustable carrierenvelope (C-E) phase is investigated theoretically. We consider the weak-field regime where tunneling processes and multiphoton ionization are negligible. It is shown that the upper state population exhibits a strong dependence on the C-E phase and on the time of arrival of the few-cycle pulse if the system is initially prepared in a coherent superposition state. We demonstrate that this effect can be employed to probe the coherence properties of the superposition state and allows one to determine the phase of the laser that prepares this state. © 2009 Optical Society of America.

## Dynamical control of pulse propagation in electromagnetically induced transparency

Physical Review A - Atomic, Molecular, and Optical Physics **79** (2009)

The influence of a phase-modulated control field on the phenomenon of electromagnetically induced transparency (EIT) is investigated theoretically. We show that the phase modulation changes the dispersive properties of the medium considerably since it results in temporal oscillations of the transparency window in frequency space. This is in marked contrast to the standard EIT setup, where the transparency window is fixed and determined by the two-photon resonance condition. In particular, we find that the phase modulation enables the propagation of probe pulses with disjoint frequency spectra at different times and allows the shifting of the central frequency of a probe pulse almost without distortion of its shape. We employ the time-dependent susceptibility of the medium to explain and analyze our results and demonstrate that this concept yields qualitative as well as quantitative agreement with the numerical integration of Maxwell-Bloch equations. Our theoretical model can be applied to other media with time-dependent susceptibilities. © 2009 The American Physical Society.

## Resonant interferometric lithography beyond the diffraction limit

Optics InfoBase Conference Papers (2009)

## Resonant interferometric lithography beyond the diffraction limit

Optics InfoBase Conference Papers (2009)

## Resonant interferometric lithography beyond the diffraction limit

Physical Review Letters **100** (2008)

A novel approach for the generation of subwavelength structures in interferometric optical lithography is described. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. Since this process only comprises resonant atom-field interactions, a multiphoton absorption medium is not required. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at very low laser intensities. © 2008 The American Physical Society.