Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z33: Open Quantum Systems IIIFocus Recordings Available

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Sponsoring Units: DAMOP Chair: Ricardo GutierrezJauregui, Columbia University Room: McCormick Place W192C 
Friday, March 18, 2022 11:30AM  11:42AM 
Z33.00001: Unidirectional transport of light along an atomic waveguide Ricardo GutierrezJauregui, Ana AsenjoGarcia Optical isolators that permit transport of light in one direction and block it in the opposite are a subject of considerable interest. Motivated by a recent prediction to engineer the dispersion relation of a waveguide constructed from atomic components, the possibility to create directional transport in an open, collective quantum system can now be explored. In this talk I will review an idealized model for an atomic chain whose optical response is engineered to display directionality. I will discuss a scattering formulation where modetomode transmissions are readily calculated to fully characterize the optical response. Once the conditions for directionality are established, I explore how to retrieve excitations efficiently from a directional chain. To finish, I will include the effect of imperfections that break the periodicity of the array and show that backscattering is suppressed even in the presence of strong noise for a directional chain. 
Friday, March 18, 2022 11:42AM  11:54AM 
Z33.00002: Doubledriven ParityTime (PT) and AntiParityTime (APT) Symmetric Floquet Models Julia Cen, Yogesh N Joglekar, Avadh B Saxena In quantum mechanics, one of the key requirements for a system is that it must be Hermitian in order to have real energies and unitary time evolution. Over the past two decades, we have seen tremendous growth of interest in systems that are nonHermitian, but PTsymmetric. This is due to the fact they have been found to possess real energies, although being open systems, hence generalizing the Hermiticity condition. More recently, there has been increasing interest in nonHermitian systems with APTsymmetry, which has also been found in many contexts such as optics, diffusive systems, and electronics. In this talk, we will explore various types of single and doubledriven timeperiodic nonHermitian PT and APTsymmetric Hamiltonians. Timedependent systems are generally difficult to solve, but being timeperiodic, we can resort to using Floquet theory for our models. PT and APT symmetries in the models give rise to transitions of PTsymmetry breaking and restoring, which as a result leads to observations of many fascinating and rich features and characteristics not seen in Hermitian cases. This could bring about new exciting developments to the probing and control of quantum systems. 
Friday, March 18, 2022 11:54AM  12:06PM 
Z33.00003: Protocols for cooling with reservoirs strongly coupled to a system Azadeh Mazloom, James K Freericks In conventional theories of reservoirs coupled to systems, the reservoir is infinitely large and couples with an infinitesimally small coupling to the system. This allows it to exchange energy without modifying the properties of the system, ultimately leading to thermal equilibrium. In quantum computing, we would like to design cooling qubits that rapidly cool a system. But, because we only have a small number of qubits available, we must couple the reservoir strongly to the system. An iontrap simulator is ideal for examining this behavior. We consider the ions at the end as the reservoir and the ions in the center as the system. It is a transversefield Ising model with longrange interactions, which creates a strongly coupled reservoirsystem. Our protocol is to start the bath sites in a lowenergy state, wait, and then reset them back to a lowenergy state at specific times. We show that this procedure makes the middle system reach close to its ground state. The efficiency of such cooling strongly depends on the reset rate and the strength of the systembath coupling. By looking into the average of the spin, both along the Ising coupling direction and along the field direction, we can optimally predict the reset times in order to evolve the system closer to the ground state. 
Friday, March 18, 2022 12:06PM  12:18PM 
Z33.00004: Locality of physical noise in quantum rigid rotors Shubham Jain, Victor V Albert Molecular rotational state spaces, modeled by infinite dimensional Hilbert spaces of quantum rigid rotors, present new grounds for encoding qubits with reliable error correction. They are, however, prone to noise induced by the environment via rotational friction and diffusion. As a step towards making qubits realizable through these rotor space configurations, we study the nature of noise introduced by a thermal environment in these systems. For the simpler setting of a planar rotor, we confirm that physical errors are local in the rotor's angular position and momentum phase space. Our analysis can be extended to the more general case of the completely asymmetric rigid rotor whose basis states are described by elements of the nonabelian group SO(3). 
Friday, March 18, 2022 12:18PM  12:30PM 
Z33.00005: Exact description of quantum stochastic models as quantum resistors João S Ferreira, Tony Jin, Michele Filippone, Thierry Giamarchi Diffusion is one of the most common transport phenomena at hydrodynamic scales, both in classical and quantum systems. Yet, how exactly diffusion emerges from the underlying microscopic theory in a quantum system is still an exciting open question. In this talk, we present a new method to derive the transport properties of diffusive/ohmic quantum systems connected to fermionic reservoirs. The method is based on the expansion of the current in terms of the inverse system size using Keldysh formalism. We apply it to a large class of exactly solvable quantum stochastic Hamiltonians (QSHs) with time and spacedependent noise. These models confirm the validity of our system size expansion ansatz and its efficiency in capturing the transport properties. In particular, we consider three fermionic models: i) a model with local dephasing ii) the quantum simple symmetric exclusion process model iii) a model with longrange stochastic hopping. As a byproduct, our approach equally describes the mean behavior of quantum systems under continuous measurement. 
Friday, March 18, 2022 12:30PM  1:06PM 
Z33.00006: Measuring the Earth's rotation using a chipscale Brillouin laser gyroscope Invited Speaker: Kerry J Vahala Counterpropagating lightwaves within a closed rotating loop enable rotation measurement as a result of the Sagnac effect. And modern optical gyroscopes use long coiled optical fiber paths (fiber optic gyroscopes) or resonant recirculation (ring laser gyroscopes) to greatly enhance this effect. In recent years, the possibility of chipbased optical gyroscopes has garnered considerable attention. Such integrated optical gyrocopes could enjoy the advantages of integration and scalable manufacturing, and would offer rugged designs for operation in challenging environments. Compact or chipbased ring laser gyroscopes, passive resonant gyroscopes, and interferometric gyroscopes have been reported. Here we first review some of the enabling technologies of chipintegrated designs, overview recent results, and then focus on a chipbased laser gyroscope that has been used to measure the Earth's rotation. The sensitivity of the gyroscope is limited by fundamental noise sources that are discussed. Also, operation of the gyroscope near an exceptional point is possible and the features of this mode of operation are reviewed. 
Friday, March 18, 2022 1:06PM  1:18PM 
Z33.00007: Giant atoms in onedimensional structured environments Ariadna Soro Álvarez, Carlos Sánchez Μuñoz, Anton Frisk Kockum Giant atoms (GAs) constitute a new paradigm in quantum optics in which they break the dipole approximation by coupling to light at multiple discrete points. They have been increasingly attracting attention for their ability to interact via a waveguide without decohering, which is why most previous work has been limited to GAs coupled to a onedimensional (1D) continuous waveguide. Here, we instead consider GAs coupled to a 1D structured bath, e.g., an array of coupled cavities or a photonic crystal waveguide. This environment gives rise to a band structure, where atomic decay and interaction are highly dependent on the energy band to which the atoms are tuned. In particular, we study nonMarkovian decay, time delay effects, formation of bound states and decoherencefree interaction, and we analyze how these phenomena are influenced by the number and distance of the GAs' coupling points to the bath. 
Friday, March 18, 2022 1:18PM  1:30PM 
Z33.00008: Criticality and phase classification for quadratic open quantum manybody systems Yikang Zhang, Thomas Barthel We study the steady states of translationinvariant open manybody systems governed by Lindblad master equations, where the Hamiltonian is quadratic in the ladder operators, and the Lindblad operators are either linear or quadratic and Hermitian. We find that onedimensional systems with shortrange interactions cannot be critical, i.e., steadystate correlations necessarily decay exponentially. For the quasifree case without quadratic Lindblad operators, we show that fermionic systems with shortrange interactions are noncritical for any number of spatial dimensions and provide upper bounds on the correlation lengths. Lastly, we address the question of phase transitions in quadratic fermionic systems and find that, without symmetry constraints beyond particlehole symmetries, all gapped Liouvillians belong to the same phase. 
Friday, March 18, 2022 1:30PM  1:42PM 
Z33.00009: Nonreciprocal quantum interactions without real or synthetic magnetic fields Yuxin Wang, Aashish Clerk Nonreciprocal elements are a valuable resource in realizing scalable quantum circuits and networks. Conventional routes to nonreciprocity make crucial use of external magnetic fields or synthetic gauge fields (engineered, e.g., by dynamic modulation [1,2]). In the quantum case, the corresponding nonreciprocal interactions are ultimately described by a cascaded quantumsystems master equation [3,4]. Here, we discuss an alternate route to quantum nonreciprocity that does not necessarily require external magnetic fields (real or synthetic), and whose quantum dynamics is not described by a standard cascaded master equation. We show how an example of this dynamics can be realized in a regular circuit QED setup involving two cavities and a dispersively coupled qubit. We also show how this dynamics enables a number of new applications in quantum information processing, including a novel class of dissipative single and twoqubit gates. Our ideas could be readily implemented in stateoftheart superconducting qubit setups. 
Friday, March 18, 2022 1:42PM  1:54PM 
Z33.00010: Nonequilibrium scalar field dynamics starting from Fock states: Absence of thermalization in one dimensional phonons coupled to fermions Md Mursalin Islam, Rajdeep Sensarma We propose a new method to study nonequilibrium dynamics of scalar fields starting from nonGaussian initial conditions using Keldysh field theory. We use it to study dynamics of phonons coupled to noninteracting bosonic and fermionic baths, starting from initial Fock states. We find that in one dimension long wavelength phonons coupled to fermionic baths do not thermalize both at low and high bath temperatures. At low temperature, constraints from energymomentum conservation lead to a narrow bandwidth of particlehole excitations and the phonons effectively do not see this bath. On the other hand, the strong band edge divergence of particlehole density of states leads to an undamped ``polaritonlike'' mode of the dressed phonons above the band edge of the particlehole excitations. These undamped modes contribute to the lack of thermalization of long wavelength phonons at high temperatures. In higher dimensions, these constraints and the divergence of density of states are weakened and leads to thermalization at all wavelengths. 
Friday, March 18, 2022 1:54PM  2:06PM 
Z33.00011: Universal properties of dissipative TomonagaLuttinger liquids Kazuki Yamamoto, Masaya Nakagawa, Masaki Tezuka, Masahito Ueda, Norio Kawakami In recent years, open quantum systems have been actively studied both experimentally and theoretically, as exemplified by drivendissipative systems and nonHermitian (NH) quantum systems. In this talk, we demonstrate the universal properties of dissipative TomonagaLuttinger (TL) liquids by deriving correlation functions and performing finitesize scaling analysis for a NH XXZ spin chain as a prototypical correlated model in onedimensional open quantum systems [1]. Our calculation is based analytically on the field theory, the finitesize scaling approach in conformal field theory, and the Betheansatz solution, and numerically on the densitymatrix renormalization group analysis generalized to NH systems (NHDMRG). Importantly, we uncover that the model belongs to the universality class characterized by the complexvalued TL parameter in the massless regime with weak dissipation. On the other hand, the discrepancy in the TL parameter obtained by NHDMRG and the Betheansatz analysis indicates that the model becomes massive for strong dissipation. Our results can be tested in ultracold atoms by introducing twobody loss to the BoseHubbard model with photoassociation techniques [2]. 
Friday, March 18, 2022 2:06PM  2:18PM 
Z33.00012: Timedelayed quantum feedback using a lattice of dissipative oscillators Xin Zhang, Sabine H. L. Klapp, Anja Metelmann Timedelayed quantum feedback has been a commonly used controlling method in quantum systems. However, solutions to these systems have been difficult to obtain due to their nonMarkovian nature. Here, we show that timedelayed quantum feedback can be introduced with a novel setup, which is composed of a lattice of dissipative oscillators. This approach provides a novel viewpoint of timedelayed quantum dynamics and gives us accessibility to unexplored regimes. Further, with more tunability, it could find applications in quantum information processing. 
Friday, March 18, 2022 2:18PM  2:30PM 
Z33.00013: QMARINA: Quantum Mapping Algorithm for a Resonator Interacting with N Atoms Marina Radulaski, Marina Krstic Marinkovic TavisCummings (TC) cavity quantum electrodynamical effects in the low excitation regime are at the core of atomic, optical and solid state physics. The classical modeling of the open quantum TC systems is often limited to lowdimensional Hilbert spaces. Mapping this dynamic to a quantum circuit can expand the size of the system proportionally to the number of available qubits. We develop a gatebased quantum algorithm that simulates a system of two atoms in a resonant cavity. Subsequently, we devise a recipe for a quantum circuit that can model open quantum TC system of an arbitrary size. 
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