arXiv subjects

Hakan E. Türeci

Publications and source records attributed to Hakan E. Türeci.

52 records · Page 3Linked to original sources

arXiv2014

Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks

The quantum dynamics of open many-body systems poses a challenge for computational approaches. Here we develop a stochastic scheme based on the positive P phase-space representation to study the nonequilibrium dynamics of coupled spin-boson networks that are driven and dissipative. Such problems are at the forefront of experimental research in cavity and solid state realizations of quantum optics, as well as cold atom physics, trapped ions and superconducting circuits. We demonstrate and test our method on a driven, dissipative two-site system, each site involving a spin coupled to a photonic mode, with photons hopping between the sites, where we find good agreement with Monte Carlo Wavefunction simulations. In addition to numerically reproducing features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we also predict a novel steady state quantum dynamical phase transition for an asymmetric configuration of drive and dissipation.

quant-ph↗

arXiv2014

Observation of a Dissipation-Induced Classical to Quantum Transition

We report here the experimental observation of a dynamical quantum phase transition in a strongly interacting open photonic system. The system studied, comprising a Jaynes-Cummings dimer realized on a superconducting circuit platform, exhibits a dissipation driven localization transition. Signatures of the transition in the homodyne signal and photon number reveal this transition to be from a regime of classical oscillations into a macroscopically self-trapped state manifesting revivals, a fundamentally quantum phenomenon. This experiment also demonstrates a small-scale realization of a new class of quantum simulator, whose well controlled coherent and dissipative dynamics is suited to the study of quantum many-body phenomena out of equilibrium.

quant-ph↗

arXiv2014

Self-protected polariton states in photonic quantum metamaterials

We investigate the single-photon transport properties of a one-dimensional coupled cavity array (CCA) containing a single qubit in its central site by coupling the CCA to two transmission lines supporting propagating bosonic modes with linear dispersion. We find that even in the nominally weak light-matter coupling regime, the transmission through a long array exhibits two ultra-narrow resonances corresponding to long-lived self-protected polaritonic states localized around the site containing the qubit. The lifetime of these states is found to increase exponentially with the number of array sites in sharp distinction to the polaritonic Bloch modes of the cavity array.

quant-ph↗

arXiv2014

Cavity-coupled double-quantum dot at finite bias: analogy with lasers and beyond

We present a theoretical and experimental study of photonic and electronic transport properties of a voltage biased InAs semiconductor double quantum dot (DQD) that is dipole-coupled to a superconducting transmission line resonator. We obtain the Master equation for the reduced density matrix of the coupled system of cavity photons and DQD electrons accounting systematically for both the presence of phonons and the effect of leads at finite voltage bias. We subsequently derive analytical expressions for transmission, phase response, photon number and the non-equilibrium steady state electron current. We show that the coupled system under finite bias realizes an unconventional version of a single-atom laser and analyze the spectrum and the statistics of the photon flux leaving the cavity. In the transmission mode, the system behaves as a saturable single-atom amplifier for the incoming photon flux. Finally, we show that the back action of the photon emission on the steady-state current can be substantial. Our analytical results are compared to exact Master equation results establishing regimes of validity of various analytical models. We compare our findings to available experimental measurements.

cond-mat.mes-hall↗

arXiv2013

Cavity-mediated near-critical dissipative dynamics of a driven condensate

We investigate the near-critical dynamics of atomic density fluctuations in the non-equilibrium self-organization transition of an optically driven quantum gas coupled to a single mode of a cavity. In this system cavity-mediated long-range interactions between atoms, tunable by the drive strength, lead to softening of an excitation mode recently observed in experiments. This phenomenon has previously been studied within a two-mode approximation for the collective motional degrees of freedom of the atomic condensate which results in an effective open-system Dicke model. Here, including the full spectrum of atomic modes we find a finite lifetime for a roton-like mode in the Bogoliubov excitation spectrum that is strongly pump-dependent. The corresponding decay rate and critical exponents for the phase-transition are calculated explaining the non-monotonic pump-dependent atomic damping rate observed in recent experiments. We compute the near-critical behavior of the intra-cavity field fluctuations, that has been previously shown to be enhanced with respect to the equilibrium Dicke model in a two-mode approximation. We highlight the role of the finite size of the system in the suppression of it below the expectations of the open Dicke model.

cond-mat.quant-gas↗

arXiv2012

Non-equilibrium dynamics of coupled qubit-cavity arrays

We study the coherence and fluorescence properties of the coherently pumped and dissipative Jaynes-Cummings-Hubbard model describing polaritons in a coupled-cavity array. At weak hopping we find strong signatures of photon blockade similar to single-cavity systems. At strong hopping the state of the photons in the array depends on its size. While the photon blockade persists in a dimer consisting of two coupled cavities, a coherent state forms on an extended lattice, which can be described in terms of a semi-classical model.

cond-mat.quant-gas↗

arXiv2011

Quantum quench of Kondo correlations in optical absorption

The interaction between a single confined spin and the spins of a Fermionic reservoir leads to one of the most spectacular phenomena of many body physics -- the Kondo effect. Here we report the observation of Kondo correlations in optical absorption measurements on a single semiconductor quantum dot tunnel-coupled to a degenerate electron gas. In stark contrast to transport experiments, absorption of a single photon leads to an abrupt change in the system Hamiltonian and a quantum quench of Kondo correlations. By inferring the characteristic power law exponents from the experimental absorption line-shapes, we find a unique signature of the quench in the form of an Anderson orthogonality catastrophe, originating from a vanishing overlap between the initial and final many-body wave-functions. We also show that the power-law exponents that determine the degree of orthogonality can be tuned by applying an external magnetic field which gradually turns the Kondo correlations off. Our experiments demonstrate that optical measurements on single artificial atoms offer new perspectives on many-body phenomena previously studied exclusively using transport spectroscopy. Moreover, they initiate a new paradigm for quantum optics where many-body physics influences electric field and intensity correlations.

cond-mat.mes-hall↗

arXiv2009

Solid-State Spin-Photon Quantum Interface without Spin-Orbit Coupling

We show that coherent optical manipulation of a single confined spin is possible even in the absence of spin-orbit coupling. To this end, we consider the non-Markovian dynamics of a single valence orbital hole spin that has optically induced spin exchange coupling to a low temperature partially polarized electron gas. We show that the fermionic nature of the reservoir induces a coherent component to the hole spin dynamics that does not generate entanglement with the reservoir modes. We analyze in detail the competition of this reservoir-assisted coherent contribution with dissipative components displaying markedly different behavior at different time scales and determine the fidelity of optically controlled spin rotations.

cond-mat.mes-hall↗

arXiv2009

Shedding light on non-equilibrium dynamics of a spin coupled to fermionic reservoir

A single confined spin interacting with a solid-state environment has emerged as one of the fundamental paradigms of mesoscopic physics. In contrast to standard quantum optical systems, decoherence that stems from these interactions can in general not be treated using the Born-Markov approximation at low temperatures. Here we study the non-equilibrium dynamics of a single-spin in a semiconductor quantum dot adjacent to a fermionic reservoir and show how the dynamics can be revealed in detail in an optical absorption experiment. We show that the highly asymmetrical optical absorption lineshape of the resulting Kondo exciton consists of three distinct frequency domains, corresponding to short, intermediate and long times after the initial excitation, which are in turn described by the three fixed points of the single-impurity Anderson Hamiltonian. The zero-temperature power-law singularity dominating the lineshape is linked to dynamically generated Kondo correlations in the photo-excited state. We show that this power-law singularity is tunable with gate voltage and magnetic field, and universal.

cond-mat.str-el↗

arXiv2009

Ab initio self-consistent laser theory and random lasers

We review our recent work leading to steady-state solutions of the semiclassical (Maxwell-Bloch) equations of a laser. These are coupled non-linear partial differential equations in space and time which have previously been solved either by fully time-dependent numerical simulations or by using major approximations which neglect non-linear modal interactions and/or the openness of the laser system. We have found a time-independent technique for determining these stationary solutions which can treat lasers of arbitrary complexity and degree of openness. Our method has been shown to agree with time-dependent numerical solutions to high accuracy and has been applied to find the electric field patterns (lasing modes) of random lasers, which lack a laser cavity and are so strongly damped that the linear system has no detectable resonances. Our work provides a link between an important non-linear wave system and the field of quantum/wave chaos in linear systems.

physics.optics↗

arXiv2008

Quantitative Verification of Ab Initio Self-consistent Laser Theory

We generalize and test the recent "ab initio" self-consistent (AISC) time-independent semiclassical laser theory. This self-consistent formalism generates all the stationary lasing properties in the multimode regime (frequencies, thresholds, internal and external fields, output power and emission pattern) from simple inputs: the dielectric function of the passive cavity, the atomic transition frequency, and the transverse relaxation time of the lasing transition. We find that the theory gives excellent quantitative agreement with full time-dependent simulations of the Maxwell-Bloch equations after it has been generalized to drop the slowly-varying envelope approximation. The theory is infinite order in the non-linear hole-burning interaction; the widely used third order approximation is shown to fail badly.

physics.optics↗

arXiv2008

Non-Markovian decoherence of localized nanotube excitons by acoustic phonons

We demonstrate that electron-phonon interaction in quantum dots embedded in one-dimensional systems leads to pronounced, non-Markovian decoherence of optical transitions. The experiments we present focus on the lineshape of photoluminescence from low-temperature axially localized carbon nanotube excitons. The independent boson model that we use to model the phonon interactions reproduces with very high accuracy the broad and asymmetric emission lines and the weak red-detuned radial breathing mode replicas observed in the experiments. The intrinsic phonon-induced pure-dephasing of the zero-phonon line is two orders of magnitude larger than the lifetime broadening and is a hallmark of the reduced dimensionality of the phonon bath. The non-Markovian nature of this decoherence mechanism may have adverse consequences for applications of one-dimensional systems in quantum information processing.

cond-mat.mes-hall↗

arXiv2008

Strong Interactions in Multimode Random Lasers

Unlike conventional lasers, diffusive random lasers (DRLs) have no resonator to trap light and no high-Q resonances to support lasing. Due to this lack of sharp resonances the DRL has presented a challenge to conventional laser theory. We present a theory able to treat the DRL rigorously, and provide results on the lasing spectra, internal fields and output intensities of DRLs. Typically DRLs are highly multimode lasers, emitting light at a number of wavelengths. We show that the modal interactions through the gain medium in such lasers are extremely strong and lead to a uniformly spaced frequency spectrum, in agreement with recent experimental observations.

physics.optics↗

arXiv2008

Interacting Quantum Dot Coupled to a Kondo Spin: A Universal Hamiltonian Study

We study a mesoscopic interacting quantum dot described by the "universal Hamiltonian" that is coupled to a Kondo spin. The ferromagnetic exchange interaction within the dot leads to a stepwise increase of the ground state spin; this Stoner staircase is modified non-trivially by the Kondo interaction. We find that the spin-transition steps move to lower values of the exchange coupling for weak Kondo interaction, but shift back up for sufficiently strong Kondo coupling. The problem is solved numerically by diagonalizing the system Hamiltonian in a customized good-spin basis and analytically in the weak and strong Kondo coupling limits. The interplay of Kondo and ferromagnetic exchange can be probed with experimentally tunable parameters.

cond-mat.mes-hall↗

arXiv2006

Coherent optical manipulation of triplet-singlet states in coupled quantum dots

We show that spin-orbit coupling in a quantum dot molecule allows for coherent manipulation of two electron spin states using Raman transitions. Such two-electron spin states defined by the singlet and triplet states of two exchange coupled quantum dots can have favorable coherence properties. In addition, two of the four metastable ground states in this system can be used as auxiliary states that could facilitate implementation of tasks such as mapping of spin states to that of a single propagating photon. We find that even weak spin-orbit effects -- manifesting themselves as slightly different g-factors for the electron and the hole -- would allow for the coherent Raman coupling of the singlet-triplet states. We also discuss the possibilities for implementing quantum optical techniques for spin preparation and manipulation.

cond-mat.mes-hall↗

arXiv2006

Theory of the spatial structure of non-linear lasing modes

A self-consistent integral equation is formulated and solved iteratively which determines the steady-state lasing modes of open multi-mode lasers. These modes are naturally decomposed in terms of frequency dependent biorthogonal modes of a linear wave equation and not in terms of resonances of the cold cavity. A one-dimensional cavity laser is analyzed and the lasing mode is found to have non-trivial spatial structure even in the single-mode limit. In the multi-mode regime spatial hole-burning and mode competition is treated exactly. The formalism generalizes to complex, chaotic and random laser media.

cond-mat.mes-hall↗