Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R44: SYK and Quantum Circuit ModelsLive
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Aavishkar Patel, University of California, Berkeley |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R44.00001: Excitation spectra of quantum matter without quasiparticles I: Sachdev-Ye-Kitaev models Maria Tikhanovskaya, Haoyu Guo, Subir Sachdev, Grigory Tarnopolsky We study the low frequency spectra of complex Sachdev-Ye-Kitaev (SYK) models at general densities.The analysis applies also to SU(M) magnets with random exchange at large M. The spectral densitiesare computed by numerical analysis of the saddle point equations on the real frequency axis at zero temperature (T). The asymptotic low frequency behaviors are found to be in excellent agreement with the scaling dimensions of irrelevant operators which perturb the conformally invariant critical states. Of possible experimental interest is our computation of the universal spin spectral weight of the SU(M) magnets at low frequency and temperature: this includes a contribution from the time reparameterization mode, which is the boundary graviton of the holographic dual. This analysis is extended to a random t-J model in a companion paper. |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R44.00002: Deconfined metallic criticality and Sachdev-Ye-Kitaev physics of spin-1/2 electrons at finite doping Philipp Dumitrescu, Nils Wentzell, Olivier Parcollet, Antoine Georges We establish the phase diagram of doped spin-1/2 electrons on a fully connected lattice with random hopping, that are interacting through a random Heisenberg spin exchange as well as finite onsite Hubbard repulsion. Using quantum Monte Carlo simulations in an extended dynamical mean-field theory framework, we show the existence of a quantum critical point which separates two different metallic phases -- a metallic spin-glass phase at low doping and a Fermi liquid at large doping. At the critical doping and finite temperatures, we find non-Fermi liquid scaling of electrons and spin correlation functions; the latter is similar to that of scaling in Sachdev-Ye-Kitaev models. We compare our results to recent renormalization group treatments. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R44.00003: Sachdev-Ye-Kitaev superconductivity: Quantum Kuramoto and generalized Richardson models Hanteng Wang, Alexander Chudnovskiy, Alexander Gorsky, Alex Kamenev The Sachdev-Ye-Kitaev (SYK) model has emerged as a new paradigm of non-Fermi-liquid behavior. Here we investigate a possibility of having a superconducting off-diagonal long-range order (ODLRO) and a pseudogap phase within the SYK framework. We found that ODLRO may be established in a spin-1/2 version of the model with the time-reversal invariance and an extra attractive interaction. If the latter is taken as the on-site negative U Hubbard term, it leads to the pseudogap phase at U < Uc dominated by quantum fluctuations of local phases. These fluctuations are described by a quantum version of the Kuramoto model, traditionally employed to illustrate synchronization of classical nonlinear oscillators. In the opposite limit of large U, the SYK + Hubbard model is approaching a certain generalization of the integrable Richardson model. We present exact diagonalization studies, along with analytic solutions of the aforementioned limiting cases. We also discuss possible holographic interpretations of the model, ODLRO, and the pseudogap. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R44.00004: Dirac fast scrambers Jaewon Kim, Ehud Altman, Xiangyu Cao We introduce a family of Gross-Neveu-Yukawa models with a large number of fermion and boson flavors as higher dimensional generalizations of the Sachdev-Ye-Kitaev model. The models may be derived from local lattice couplings and give rise to Lorentz invariant critical solutions in 1+1 and 2+1 dimensions. These solutions imply anomalous dimensions of both bosons and fermions tuned by the number ratio of boson to fermion flavors. In 1+1 dimension the solution represents a stable critical phase, while in 2+1 dimension it governs a quantum phase transition. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R44.00005: SYK criticality and spin glass order in the random doped Heisenberg model Alexander Wietek, Henry Shackleton, Antoine Georges, Subir Sachdev We investigate the t-J model of electrons with fully connected random hoppings and exchange interactions. Using numerical exact diagonalization and the thermal pure quantum state method, we establish the extent of the spin glass ordered known to be present at half-filling is stable to non-zero hole doping, up to a critical hole-doping of around $p_c =1/3$. Our simulations reveal a maximum of the thermodynamic entropy at finite temperature as well as a maximum of the entanglement entropy at zero temperature close to $p_c$. The quasiparticle spectral density is found to obey the analog of the Fermi liquid Luttinger relation only for p > p_c. We note connections to SYK criticality and the hole-doped cuprates. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R44.00006: Novel phases of quantum circuits protected by hidden dynamical symmetries Yimu Bao, Soonwon Choi, Ehud Altman States evolving in quantum circuits are known to undergo measurement-induced phase transitions from volume-law to area-law entanglement. We argue that many more phases are possible. This statement is made precise in a broad class of circuits, for which we can map the steady state of information dynamics to the ground states of an effective Hamiltonian, possessing a larger symmetry than the symmetry of the physical circuit. The different ground states admitted by the larger effective symmetry, including broken symmetry and SPT phases, correspond to distinct patterns of information flow and scrambling in the circuit. We will illustrate these ideas using two examples. First, we show that the dynamics of spin systems having only Z_2 symmetry, generally map to the ground states of an effective Hamiltonian with D_4 (non-abelian) symmetry. We discuss the physical meaning of the different phases in terms of the information flow and scrambling in the circuit. Second, we show that quadratic fermion circuits, preserving only fermion parity, map to an effective Hamiltonian with U(1) symmetry. We consequently predict a measurement-induced KT transition between a critical phase with log(L) entanglement and a "trivial" area-law phase. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R44.00007: Algorithmic cooling for holographic quantum circuits Galit Anikeeva, Patrick Hayden, Isaac H Kim Quantum computers are capable of efficiently contracting unitary tensor networks, a task that is likely to remain difficult for classical computers. A particularly promising subclass of such networks is holographic; these networks can be contracted on a small quantum computer to aid a simulation of a large quantum system. However, without an ability to selectively reset a subset of qubits, the associated spatial cost can be exorbitant. In this paper, we propose a protocol that can unitarily reset the qubits, thus dramatically reducing the requisite spatial cost to implement the contraction algorithm on general near-term quantum computers. This protocol generates fresh qubits from the used ones, by partially applying the time-reversed quantum circuit over the qubits that are no longer in use. In the absence of noise, we prove that the state of a subset of these qubits becomes |0...0>, up to an error exponentially small in the number of gates applied. We also provide a numerical evidence that the protocol works in the presence of noise. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R44.00008: Criticality and entanglement in non-unitary quantum circuits and tensor networks of non-interacting fermions Chao-Ming Jian, Bela Bauer, Anna Keselman, Andreas W Ludwig There is a correspondence between tensor networks on a (d+ 1)-dimensional lattice and local non-unitary quantum circuits acting on d-dimensional systems. The latter is closely related to circuits composed of unitary evolution and measurements. We show that in the case of non-interacting fermions, there is a further correspondence between non-unitary circuits in d spatial dimensions and non-interacting fermion problems with static Hamiltonians in (d+1) spatial dimensions. Via these correspondences, the non-unitary circuits and their corresponding tensor network can be classified by the generic symmetries of this non-interacting Hamiltonian. Moreover, critical behaviors in random non-unitary quantum circuits can be generically connected to the criticality of non-interacting fermions under quenched disorder. To exemplify this, we numerically study the quantum states at the boundary of Haar-random Gaussian fermionic tensor networks of dimension D= 2 and D= 3. We show that the most general such tensor network ensemble corresponds to a unitary problem of fermions with static disorders in symmetry class DIII, which for both D= 2 and D= 3 is known to exhibit a stable critical metallic phase. Tensor networks in all other symmetry classes can also be systematically constructed. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R44.00009: Emergent Lie Algebra and Quantum information dynamics in Brownian SYK models Lakshya Agarwal, Shenglong Xu The out-of-time ordered correlator plays an important role in understanding how the information of the initial state scrambles over the entire system under unitary time evolution. Incorporating additional symmetries, such as charge conservation, can have profound effects on information scrambling. We study the out-of-time ordered correlator of generic chaotic systems with charge conservation, using the Brownian SYK models as examples. We show that the averaging of the uncorrelated random couplings at different times gives rise to an emergent SU(2) x SU(2) algebra structure in the Super-Hamiltonian, which is enlarged to SU(4) when charge conservation is included. The algebra structure drastically reduces the size of the Hilbert space from exponential to linear in N, providing us full access to the quantum dynamics away from the large N limit, where the quantum fluctuations become important. The generalization of using the formalism to examine other observables and higher dimensional models will also be discussed. |
Thursday, March 18, 2021 9:48AM - 10:00AM Live |
R44.00010: Super-Poissonian behavior of the energy specrum in the non-ergodic extended regime Richard Berkovits Non-ergodic extended phase between the ergodic extended metallic phase and the localized phase has drawn much recent interest in different fields such as Such a the Sachdev-Ye-Kitaev model in high-energy physics and quantum gravity, to the interacting many-body localization in condensed matter physics and quantum computing. This phase is characterized by fractal behavior of the wavefunctions, and a postulated correlated mini-band structure of the energy spectrum. The signature in the spectra is expected on intermediate energy scales. Nevertheless, due to the Thouless energy and ambiguities in the unfolding procedure, the usual methods for characterizing these scales, e.g., rigidity or number variance, are inconclusive. We show that by using the singular value decomposition method, clear evidence for a super-Poissonian behavior in this regime emerges, for the Rosenzweig-Porter model as well as for anisotopic spin chains in the many-particle delocalized regime. This behavior is consistent with a picture of correlated mini-bands. |
Thursday, March 18, 2021 10:00AM - 10:12AM Live |
R44.00011: Excitation spectra of quantum matter without quasiparticles II: random t-J model Maria Tikhanovskaya, Haoyu Guo, Subir Sachdev, Grigory Tarnopolsky We study the low frequency spectrum of the deconfined critical state of t-J model with random exchange. The analysis is carried out in the large M limit of models with global SU(M) spin symmetry. The spectral density is computed by numerical analysis of the saddle point equations on the real frequency axis at zero temperature (T). The asymptotic low frequency behavior is found to be in excellent agreement with the scaling dimensions of irrelevant operators which perturb the conformally invariant critical states. The low T dependence of the resistivity of the t-J model is also determined by these irrelevant operators: the operator associated with the time-reparameterization mode leads to a resistivity∼T. In the large M limit, we also find a less irrelevant operator which leads to a resistivity~Ta where a<1, but with a prefactor which is significantly smaller than that of the ~T term. |
Thursday, March 18, 2021 10:12AM - 10:24AM Live |
R44.00012: Spontaneous Breaking of U(1) Symmetry in Coupled Complex Sachdev-Ye-Kitaev Models Igor R Klebanov, Alexey Milekhin, Grigory Tarnopolsky, Wenli Zhao We study two copies of the complex SYK model coupled by a quartic term preserving the U (1) × U (1) symmetry. When the coupling coefficient α lies in a certain range, the large N theory is nearly conformal. We derive the large N Dyson-Schwinger equations and show that for the coupling α outside this range, the axial U(1) symmetry is spontaneously broken at low temperatures. We support these findings by exact diagonalizations extrapolated to large N. |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R44.00013: Imbalanced coupled Sachdev-Ye-Kitaev model Sharmistha Sahoo, Rafael Haenel, Timothy Hsieh, Marcel Franz The quantum dual of an eternal traversable wormhole in AdS2 can be described by a thermo-field-double (TFD) state of two finite-temperature Sachdev-Ye-Kitaev (SYK) systems. A bilinear coupling between these two identical SYK models was shown to prepare this TFD state as a ground state [1,2]. Although this motivates realizing a quantum version of the wormhole, the identical nature of two SYK models puts a stringent condition on experimental platforms. In this talk, I will discuss a one-parameter variant of the Maldacena-Qi model that consists of two SYK systems with different strengths of interaction. Our results show that for a range of the variation parameter, the ground state, along with other key characteristics of the wormhole phase, remains intact. The relevance of this model to a previous proposal using Majorana zero modes [3] will also be discussed. [1] J Maldacena, X-L Qi, arXiv:1804.00491 (2018). [2] S Sahoo, É L-Hurtubise, S Plugge, M Franz, Phys. Rev. Research 2, 043049 (2020). [3] A Chew, A Essin, J Alicea, Phys. Rev. B 96, 121119 (2017). |
Thursday, March 18, 2021 10:36AM - 10:48AM Live |
R44.00014: Simulating quantum transport and localization using a superconducting quantum processor Amir Karamlou, Jochen Braumueller, Bharath Kannan, David K Kim, Morten Kjaergaard, Alexander Melville, Bethany Niedzielski, Youngkyu Sung, Antti Vepsäläinen, Roni Winik, Yariv Yanay, Jonilyn Yoder, Charles Tahan, Terry Philip Orlando, Simon Gustavsson, William Oliver Quantum transport plays an important role in electron and phonon conduction in interacting condensed matter systems in the presence of inelastic scattering. Using an array of superconducting qubits, we emulate a 1-dimesional and 2-dimentsional tight-binding lattice in various parameter regimes. We first observe ballistic transport in quantum random walks on a lattice with uniform site energies. Next, we study the absence of diffusion in a disordered lattice due to Anderson localization and experimentally extract the scaling of the inverse participation ratio as a proxy for the degree of localization. Finally, we simulate the tight-binding model in the presence of a dc-field, leading to Wannier-Stark localization and Bloch oscillations. |
Thursday, March 18, 2021 10:48AM - 11:00AM Live |
R44.00015: Information propagation and recovery in a many-body quantum system Jochen Braumueller, Amir Karamlou, Yariv Yanay, Bharath Kannan, David K Kim, Morten Kjaergaard, Alexander Melville, Bethany Niedzielski, Youngkyu Sung, Antti Vepsalainen, Roni Winik, Jonilyn Yoder, Terry Philip Orlando, Simon Gustavsson, Charles Tahan, William Oliver As an interacting quantum system evolves in time, any local perturbation can spread into its many degrees of freedom; this process is known as information scrambling. While the initial perturbation dissolves, its information is still encoded in the system. One way to expose this is to let the system evolve back in time, such that the original perturbation rematerializes in a Loschmidt echo. This recovery is broken when we additionally perturb the system at a time t, prior to the time reversal. We expose these dynamics with an array of strongly coupled superconducting qubits in 1d and 2d, and we experimentally observe the propagation of information in this many-body quantum system by measuring the relevant out-of-time-ordered correlators. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700