Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S27: Open Quantum Systems II |
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Sponsoring Units: DAMOP DQI Chair: Ines de Vega, Ludwig-Maximilians-Universität München Room: LACC 404B |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S27.00001: Engineering Light-Matter Interactions in Photonic Crystal Waveguides Alexander Burgers, Lucas Peng, H Jeff Kimble Integrating ultracold atoms with nanophotonics enables the exploration of new paradigms in quantum optics and many body physics. Low-loss dielectric structures can be fabricated to support guided mode light used to create stable trapping potentials for neutral atoms. The dispersion relation of a Photonic crystal waveguide structure can be engineered to study the physics of photon-mediated atom-atom interactions as well as collective atomic effects. We utilize an optical lattice transport approach to achieve high fractional filling of the trap sites and report phase sensitive delivery of the atoms with respect to the lattice period. We will also report on efforts toward trapping atoms along the photonic crystal waveguide. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S27.00002: Decoherence-free Interaction between Giant Atoms in Waveguide QED Anton Frisk Kockum, Göran Johansson, Franco Nori In quantum-optics experiments with both natural and artificial atoms, the atoms are usually small enough that they can be approximated as point-like compared to the wavelength of the electromagnetic radiation they interact with. However, superconducting qubits coupled to a meandering transmission line, or surface acoustic waves, can realize "giant artificial atoms" that couple to a bosonic field at several points which are wavelengths apart. In previous work, we have shown that a single such giant atom has a frequency-dependent relaxation rate and Lamb shift due to interference effects arising from the multiple coupling points. In the present work, we generalize this to multiple giant atoms coupled at multiple points to a 1D waveguide. We show that the waveguide can mediate pairwise exchange interactions between the atoms even though the atoms do not decay through emission to the waveguide. This is not possible with "small" atoms. We further show how this decoherence-free interaction can be designed in setups with multiple atoms to implement, e.g., a 1D chain of atoms with nearest-neighbour couplings or a collection of atoms with all-to-all connectivity. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S27.00003: Bath engineering of a fluorescing artificial atom with a photonic crystal Patrick Harrington, Mahdi Naghiloo, Jonathan Monroe, Kater Murch A quantum emitter decays due to vacuum fluctuations at its transition frequency. By virtue of the entwined nature of dissipation and fluctuations, this process can be controlled by engineering the impedance of the environment. In our experiment, a transmon qubit and a microwave photonic crystal are respectively the emitter and the engineered vacuum environment. The photonic crystal is realized by a step-impedance transmission line which, akin to a Purcell filter, structures the electromagnetic density of states by suppressing vacuum fluctuations over a frequency band. If the emitter's transition frequency is on the photonic band edge, the non-Markovian structured environment allows for drive and dissipation to produce non-trivial steady states. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S27.00004: Selective Radiance: Enhancing Atom-light Interactions via Correlated Dissipation Ana Asenjo-Garcia, Mariona Moreno-Cardoner, Andreas Albrecht, H Jeff Kimble, Darrick E. Chang Spontaneous emission, in which photons are scattered into undesired channels, limits how strongly atoms interact with preferred photonic modes. Typically, it is assumed that this scattering occurs at a rate given by a single isolated atom, which in turn gives rise to standard limits of fidelity in applications such as photonic quantum memories and quantum gates. However, this assumption is invalid when atoms are close enough to each other so that they give rise to collective subradiant states, whose free-space decay is suppressed. Inspired by subradiance, we introduce the concept of “selective radiance”. Whereas subradiant states experience a reduced coupling to all optical modes, selectively-radiant states radiate efficiently into a desired channel and very inefficiently into undesired ones. These states, which naturally appear in chains of atoms coupled to nanophotonic structures, allow for a photon storage error that performs exponentially better with number of atoms than previously known bounds. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S27.00005: Utilizing simulated atomic trajectories to aid cold atom delivery to photonic crystal waveguides Lucas Peng, Alexander Burgers, H Jeff Kimble Trapping atoms near dielectric photonics crystal waveguides (PCWs) requires novel adaptations of standard atomic physics techniques. In our current system, a conveyor belt optical lattice is utilized for transport of atoms into the photonic crystal GM trap in a “clocked” fashion. The “clocked” transmission signal contains rich information of atomic movement near the PCW. We will present numerical simulations of atomic trajectories moving in the interference and diffraction patterns of the optical lattice beams with the PCW. A calculation of the transmission signal via transfer matrix model allows us to draw comparisons between simulation and experiment. Understanding the interaction between GM traps, optical lattice conveyor belt and atoms, constitutes a significant first step towards trapping several atoms along the waveguide and observing single, and collective atomic phenomena in an engineered photonic environment. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S27.00006: Non-Markovian Dynamics in a Matter-Wave Open Quantum System Ludwig Krinner, Michael Stewart, Arturo Pazmino, Joonhyuk Kwon, Dominik Schneble One of the most fundamental examples of an open quantum system is the exponential decay of an excited two-level atom, described by the Wigner-Weisskopf model. However, the Markov approximation underlying this model can be violated under certain conditions, and recent experiments on optical decay in photonic band-gap (PBG) materials have indeed started to find deviations from its predictions. We experimentally realize a model [1,2] for an ``artificial atom'' emitting atomic matter-wave rather than optical radiation, in which the vacuum coupling and the excited-state energy can be controlled at will. The experiments are performed using an optical lattice geometry, which provides arrays of such artificial atoms. We are able to observe Markovian and strongly non-Markovian dynamics in this system, including exponential and partly reversible oscillatory decay, atom re-absorption, as well as a bound state for emission below the band edge of the mode continuum, which is a direct analog of the long-predicted atom-photon bound state in PBG-materials. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S27.00007: Spontaneous and Stimulated emission from open quantum systems Rahul Trivedi, Kevin Fischer, Shanshan Xu, Shanhui Fan, Jelena Vuckovic We provide a systematic treatment of using the input-output formalism for computing the output photon state emitted by an initially excited open quantum system coupled to a finite number of loss channels (e.g. input and output waveguides) with or without stimulation from a few-photon input pulse. The central result of this work is a connection between the state of the photons emitted by the local system and its Green's functions. We illustrate our formalism by computing the output state for a linear system, two-level system and Jaynes-Cumming system. We also extend our formalism to analyze open quantum systems coupled to a spatial continuum (e.g. free space or photonic crystals) to predict the spatial profile of few photon emissions from such systems. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S27.00008: Abrupt transition between Markovian and non-Markovian dynamics in quantum open systems Shengshi Pang, Todd Brun, Andrew Jordan Markovian dynamics of an open quantum system needs a fast decay of the bath correlation to make the evolution of the system memoryless, which usually requires a rapid restoration of the bath state. In this work, we quantitatively study how fast the the bath state needs to be restored in order to realize Markovian dynamics of an open system. We consider a simple model of a qubit system coupled to a qubit bath with the qubit bath continuously refreshed by quantum cooling. A surprising result is that there exists a threshold of the cooling rate above which the non-Markovianity of the system dynamics suddenly vanishes and the system transitions to Markovian dynamics while the decay rate of bath correlation is at the same order of the system evolution speed. This is in marked contrast to the usual understanding that Markovian quantum dynamics is generally a limiting behavior under the Born-Markov approximation, and suggests broader existence of Markovian dynamics in the quantum regime. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S27.00009: Floquet stroboscopic divisibility in non-Markovian dynamics Victor Bastidas, Thi Ha Kyaw, Jirawat Tangpanitanon, Guillermo Romero, Leong-Chuan Kwek, Dimitris Angelakis We provide a general description of a time-local master equation for a system coupled to a non-Markovian reservoir based on Floquet theory. Surprisingly, this allows us to have a divisible dynamical map at discrete times, which we refer to as Floquet stroboscopic divisibility. We illustrate the general theory by considering a Schrodinger cat coupled to both non-Markovian and Markovian baths. In the non-Markovian regime, we show the appearance of a partial stroboscopic revival of the cat at later time after its death. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S27.00010: A Case Study of Quantum Non-Markovianity: 1D Photon Scattered from a Qubit in Front of a Mirror Yao-Lung Fang, Francesco Ciccarello, Harold Baranger We propose a model system for the study of quantum non-Markovian (NM) physics. We consider a single-photon wavepacket scattered off a single two-level system strongly coupled to a one-dimensional waveguide terminated by a perfect mirror, and apply the tools of open quantum systems to investigate the NM memory effects in the scattering dynamics. By finding the exact, time-dependent solutions in both the one- and two-excitation sectors, we explicitly construct the qubit's dynamical map (DM), based on which various NM measures can be applied. For instance, the geometric measure proposed by Lorenzo, Plastina and Paternostro shows that for this system both the wavepacket width and the qubit-mirror separation contribute to the non-Markovianity. Our "scattering DM" is different from that for spontaneous emission in that the determinant of our DM can become negative. This suggests interesting features that call for further study of scattering setups. Ref: arXiv:1707.05946 |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S27.00011: Power law tails and non Markovian dynamics in open quantum systems: An exact solution from Keldysh field theory Ahana Chakraborty, Rajdeep Sensarma The Born-Markov approximation is widely used to study dynamics of open quantum systems coupled to external baths. Using Keldysh formalism, we show that the dynamics of a system of bosons (fermions) linearly coupled to non-interacting bosonic (fermionic) bath falls outside this paradigm if the bath spectral function has non-analyticities as a function of frequency. In this case, we show that the dissipative and noise kernels governing the dynamics have distinct power law tails. The Green's functions show a short time ``quasi'' Markovian exponential decay before crossing over to a power law tail, governed by the non-analyticity of the spectral function. We study a system of bosons (fermions) hopping on a one dimensional lattice, where each site is coupled linearly to an independent bath of non-interacting bosons (fermions). While the density and current profiles show interesting quantitative deviations from Markovian results, the current-current correlators show qualitatively distinct long time power law tails |t-t'|^{-3} characteristic of non-Markovian dynamics. We show that the power law decays survive in presence of inter-particle interaction in the system, but the cross-over time scale is shifted to larger values with increasing interaction strength. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S27.00012: Second Phase Transition in an Open-System Dicke Model with Spontaneous Emission Florentin Reiter, Susanne Yelin Spin-boson models, which describe the interaction between atoms and harmonic oscillators, lie at the heart of quantum information science. In particular the Dicke model [1] with its famous ``superradiant'' phase transition [2] constitutes a standard model in quantum optics and has been recently realized [3,4]. Adding noise to such models can lead to novel phases and allows for the observation of ``dissipative phase transitions'' in steady state [5]. We consider a finite-size open-system Dicke model with spontaneous emission. In this model, the superradiant phase transition can be observed in steady-state. In addition, we find a second phase transition which solely occurs in the harmonic oscillator and results in nonstationarity. The corresponding critical coupling exhibits a different scaling with the number of atoms compared to that of the superradiant phase transition. As a result, qualitatively different dynamics depending on the size of the system can be observed. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S27.00013: The Extended Stochastic Liouville Equation Gerard McCaul, Chris Lorenz, Lev Kantorovich We present an exact approach to the evolution of density matrices for open quantum systems coupled to a general harmonic environment. This generalises and extends previous work based on Caldeira-Leggett models and a factorised initial density matrix. In particular, this method allows more general forms of environment-system couplings and initial conditions. The result is an exact stochastic description for the evolution of an arbitrary open system from a broad class of initial conditions, which we term the Extended Stochastic Liouville Equation (ELSE). This technique allows us to consider driving open systems from a coupled equilibrium with the environment, even in the strong-coupling regime. This is demonstrated analysing a driven spin-Boson model using the ESLE. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S27.00014: Microscopic Description of Exceptional Points in Open Quantum Systems Savannah Garmon, Kazuki Kanki Exceptional points (EPs) are discrete points in the parameter space of a given dissipative system at which two or more eigenstates coalesce. In recent years, the EPs have been studied in a wide range of physical contexts, including experiments involving microwave cavities and simple electric circuits. While the eigenstate coalescence can be modeled using a simple phenomenological finite matrix, this approach ignores the continuum degrees of freedom that describe the detailed environmental influence in open systems. In this presentation, we apply an exact description starting from the microscopic Hamiltonian to show the eigenvalues are described by a characteristic fractional power expansion near the EP [Int. J. Theor. Phys. 51, 3536 (2012)]. We further show the usual diagonalization scheme fails at the EP and the Hamiltonian can only be reduced to Jordan block form [J. Math. Phys. 58, 092101 (2017)]. Finally, we briefly show that near the EP the usual exponential decay scheme is replaced by either modified exponential or pure non-exponential decay; we note the phenomenological model is incapable of predicting the non-exponential dynamics [J. Math. Phys. 58, 062101 (2017)]. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S27.00015: Strong Coupling Master Equation for Gaussian Noise Huo Chen To analyze the decoherence effects during quantum annealing, theoretical tools are needed to probe the system dynamics in the strong coupling region. We proposed a master equation for Gaussian noise based on cumulant expansion techniques. Without the usual weak coupling assumption, this approach treats the system Hamiltonian as a perturbation to the system-bath term, which is exactly solvable. The result is compared with non-interacting blip approxiation(NIBA), which is the most commonly used technique to simulate the strong coupling region. |
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