Researcher:
Hardal, Ali Ümit Cemal

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PhD Student

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Ali Ümit Cemal

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Hardal

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Hardal, Ali Ümit Cemal

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Now showing 1 - 10 of 11
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    Publication
    Dynamics of mode entanglement in a system of cavities coupled with a chiral mirror
    (Optical Society of America (OSA), 2014) N/A; N/A; Hardal, Ali Ümit Cemal; PhD Student; Graduate School of Sciences and Engineering; N/A
    We investigate the Hermitian and the non-Hermitian dynamics of the mode entanglement in two identical optical cavities coupled by a chiral mirror. By employing the non-Hermitian quantum evolution, we calculate the logarithmic negativity measure of entanglement for initially Fock, coherent, and squeezed states, separately. We verify the nonconservation of mean spin for the initially coherent and squeezed states when the coupling is nonreciprocal and report the associated spin noise for each case. We examine the effects of nonconserved symmetries on the mode correlations and determine the degree of nonreciprocal coupling to establish robust quantum entanglement.
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    PublicationOpen Access
    Discrete-time quantum walk with nitrogen-vacancy centers in diamond coupled to a superconducting flux qubit
    (American Physical Society (APS), 2013) Xue, Peng; Shikano, Yutaka; Sanders, Barry C.; Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; N/A; 1674
    We propose a quantum-electrodynamics scheme for implementing the discrete-time, coined quantum walk with the walker corresponding to the phase degree of freedom for a quasimagnon field realized in an ensemble of nitrogen-vacancy centers in diamond. The coin is realized as a superconducting flux qubit. Our scheme improves on an existing proposal for implementing quantum walks in cavity quantum electrodynamics by removing the cumbersome requirement of varying drive-pulse durations according to mean quasiparticle number. Our improvement is relevant to all indirect-coin-flip cavity quantum-electrodynamics realizations of quantum walks. Our numerical analysis shows that this scheme can realize a discrete quantum walk under realistic conditions.
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    PublicationOpen Access
    Quantum correlated heat engine with spin squeezing
    (American Physical Society (APS), 2014) Altıntaş, Ferdi; Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; N/A; 1674
    We propose a four-level quantum heat engine in an Otto cycle with a working substance of two spins subject to an external magnetic field and coupled to each other by a one-axis twisting spin squeezing nonlinear interaction. We calculate the positive work and the efficiency of the engine for different parameter regimes. In particular, we investigate the effects of quantum correlations at the end of the two isochoric processes of the Otto cycle, as measured by the entanglement of formation and quantum discord, on the work extraction and efficiency. The regimes where the quantum correlations could enhance the efficiency and work extraction are characterized.
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    PublicationOpen Access
    Renyi divergences, Bures geometry and quantum statistical thermodynamics
    (Multidisciplinary Digital Publishing Institute (MDPI), 2016) Department of Physics; Department of Physics; Müstecaplıoğlu, Özgür Esat; Hardal, Ali Ümit Cemal; Faculty Member; College of Sciences; 1674; N/A
    The Bures geometry of quantum statistical thermodynamics at thermal equilibrium is investigated by introducing the connections between the Bures angle and the Renyi 1/2-divergence. Fundamental relations concerning free energy, moments of work, and distance are established.
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    PublicationOpen Access
    Einstein-Podolsky-Rosen-type quantum entanglement between coupled cavities
    (Institute of Physics (IOP) Publishing, 2014) Department of Physics; Department of Physics; Müstecaplıoğlu, Özgür Esat; Hardal, Ali Ümit Cemal; Faculty Member; College of Sciences; 1674; N/A
    We investigate Einstein-Podolsky-Rosen (EPR)-type spatial entanglement between two coupled, driven, dissipative and nonlinear optical cavities. We identify the required parameter regimes of polariton-exchange and nonlinearity coefficients as having robust EPR-type entanglement at the steady state. In addition, we examine the influence of weak and strong drives on these parameter regimes.
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    PublicationOpen Access
    Spin squeezing, entanglement, and coherence in two driven, dissipative, nonlinear cavities coupled with single- and two-photon exchange
    (Optical Society of America (OSA), 2014) Department of Physics; Department of Physics; Müstecaplıoğlu, Özgür Esat; Hardal, Ali Ümit Cemal; Faculty Member; College of Sciences; 1674; N/A
    We investigate spin squeezing, quantum entanglement, and second-order coherence in two coupled, driven, dissipative, nonlinear cavities. We compare these quantum statistical properties for the cavities coupled with either single- or two-photon exchange. Solving the quantum optical master equation of the system numerically in the steady state, we calculate the zero-time delay second-order correlation function for the coherent, genuine two-mode entanglement parameters, an optimal spin squeezing inequality associated with particle entanglement, concurrence, quantum entropy, and logarithmic negativity. We identify regimes of distinct quantum statistical character depending on the relative strength of photon exchange and nonlinearity. Moreover, we examine the effects of weak and strong drives on these quantum statistical regimes.
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    PublicationOpen Access
    Superradiant quantum heat engine
    (Nature Publishing Group (NPG), 2015) Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; College of Sciences; N/A; 1674
    Quantum physics revolutionized classical disciplines of mechanics, statistical physics, and electrodynamics. One branch of scientific knowledge however seems untouched: thermodynamics. Major motivation behind thermodynamics is to develop efficient heat engines. Technology has a trend to miniaturize engines, reaching to quantum regimes. Development of quantum heat engines (QHEs) requires emerging field of quantum thermodynamics. Studies of QHEs debate whether quantum coherence can be used as a resource. We explore an alternative where it can function as an effective catalyst. We propose a QHE which consists of a photon gas inside an optical cavity as the working fluid and quantum coherent atomic clusters as the fuel. Utilizing the superradiance, where a cluster can radiate quadratically faster than a single atom, we show that the work output becomes proportional to the square of the number of the atoms. In addition to practical value of cranking up QHE, our result is a fundamental difference of a quantum fuel from its classical counterpart. Keywords
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    PublicationOpen Access
    Quantum heat engine with coupled superconducting resonators
    (American Physical Society (APS), 2017) Wilson, C. M.; Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; College of Sciences; N/A; 1674; N/A
    We propose a quantum heat engine composed of two superconducting transmission line resonators interacting with each other via an optomechanical-like coupling. One resonator is periodically excited by a thermal pump. The incoherently driven resonator induces coherent oscillations in the other one due to the coupling. A limit cycle, indicating finite power output, emerges in the thermodynamical phase space. The system implements an all-electrical analog of a photonic piston. Instead of mechanical motion, the power output is obtained as a coherent electrical charging in our case. We explore the differences between the quantum and classical descriptions of our system by solving the quantum master equation and classical Langevin equations. Specifically, we calculate the mean number of excitations, second-order coherence, as well as the entropy, temperature, power, and mean energy to reveal the signatures of quantum behavior in the statistical and thermodynamic properties of the system. We find evidence of a quantum enhancement in the power output of the engine at low temperatures.
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    PublicationOpen Access
    Rabi model as a quantum coherent heat engine: from quantum biology to superconducting circuits
    (American Physical Society (APS), 2015) Altıntaş, Ferdi; Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; College of Sciences; N/A; 1674
    We propose a multilevel quantum heat engine with a working medium described by a generalized Rabi model which consists of a two-level system coupled to a single-mode bosonic field. The model is constructed to be a continuum limit of a quantum biological description of light-harvesting complexes so that it can amplify quantum coherence by a mechanism which is a quantum analog of classical Huygens clocks. The engine operates in a quantum Otto cycle where the working medium is coupled to classical heat baths in the isochoric processes of the four-stroke cycle, while either the coupling strength or the resonance frequency is changed in the adiabatic stages. We found that such an engine can produce work with an efficiency close to the Carnot bound when it operates at low temperatures and in the ultrastrong-coupling regime. The interplay of the effects of quantum coherence and quantum correlations on the engine performance is discussed in terms of second-order coherence, quantum mutual information, and the logarithmic negativity of entanglement. We point out that the proposed quantum Otto engine can be implemented experimentally with modern circuit quantum electrodynamic systems where flux qubits can be coupled ultrastrongly to superconducting transmission-line resonators.
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    PublicationOpen Access
    Transfer of spin squeezing and particle entanglement between atoms and photons in coupled cavities via two-photon exchange
    (Optical Society of America (OSA), 2012) Department of Physics; Department of Physics; Hardal, Ali Ümit Cemal; Müstecaplıoğlu, Özgür Esat; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; N/A; 1674
    We examine transfer of particle entanglement and spin squeezing between atomic and photonic subsystems in optical cavities coupled by two-photon exchange. Each cavity contains a single atom, interacting with cavity photons with a two-photon cascade transition. Particle entanglement is characterized by evaluating optimal spin squeezing inequalities for the cases of initially separable and entangled two-photon states. It is found that particle entanglement is first generated among the photons in separate cavities and then transferred to the atoms. The underlying mechanism is recognized as an intercavity two-axis twisting spin squeezing interaction, induced by two-photon exchange, and its optimal combination with the intracavity atom-photon coupling. Relative effect of nonlocal two-photon exchange and local atom-photon interactions of cavity photons on the spin squeezing and entanglement transfer is pointed out.