Monday June 24th 4:30pm - 6:30pm and Tuesday June 25th 4:00pm - 6:00pm

MONDAY 6/24/24:

Presenter: Dong An, University of Maryland

Title: Multi-product Hamiltonian simulation with explicit commutator scaling

Abstract: The well-conditioned multi-product formula (MPF), proposed by [Low, Kliuchnikov, and Wiebe, 2019], is a simple high-order time-independent Hamiltonian simulation algorithm that implements a linear combination of standard product formulas of low order. While the MPF aims to simultaneously exploit commutator scaling among Hamiltonians and achieve near-optimal time and precision dependence, its lack of a rigorous error bound on the nested commutators renders its practical advantage ambiguous. In this work, we conduct a rigorous complexity analysis of the well-conditioned MPF, demonstrating explicit commutator scaling and near-optimal time and precision dependence at the same time. Using our improved complexity analysis, we present several applications of practical interest where the MPF based on a second-order product formula can achieve a polynomial speedup in both system size and evolution time, as well as an exponential speedup in precision, compared to second-order and even higher-order product formulas. Compared to post-Trotter methods, the MPF based on a second-order product formula can achieve polynomially better scaling in system size, with only poly-logarithmic overhead in evolution time and precision. (based on [arXiv:2403.08922])

Presenter: Elizabeth Bennewitz, University of Maryland

Title: Simulating Meson Scattering on Spin Quantum Simulators

Abstract: Studying high-energy collisions of composite particles, such as hadrons and nuclei, is an outstanding goal for quantum simulators. However, the preparation of hadronic wave packets has posed a significant challenge, due to the complexity of hadrons and the precise structure of wave packets. This has limited demonstrations of hadron scattering on quantum simulators to date. Observations of confinement and composite excitations in quantum spin systems have opened up the possibility to explore scattering dynamics in spin models. In this article, we develop two methods to create entangled spin states corresponding to wave packets of composite particles in analog quantum simulators of Ising spin Hamiltonians. One wave-packet preparation method uses the blockade effect enabled by beyond-nearest-neighbor Ising spin interactions. The other method utilizes a quantum-bus-mediated exchange, such as the native spin-phonon coupling in trapped-ion arrays. With a focus on trapped-ion simulators, we numerically benchmark both methods and show that high-fidelity wave packets can be achieved in near-term experiments. We numerically study the scattering of wave packets for experimentally realizable parameters in the Ising model and find inelastic-scattering regimes, corresponding to particle production in the scattering event, with prominent and distinct experimental signals. Our proposal, therefore, demonstrates the potential of observing inelastic scattering in near-term quantum simulators.

Presenter: Chung-Chun Hsieh, University of Maryland

Title: Scattering wave packets of hadrons in gauge theories: Preparation on a quantum computer

Abstract: Quantum simulation holds promise of enabling a complete description of high-energy scattering processes rooted in gauge theories of the Standard Model. A first step in such simulations is preparation of interacting hadronic wave packets. To create the wave packets, one typically resorts to adiabatic evolution to bridge between wave packets in the free theory and those in the interacting theory, rendering the simulation resource intensive. In this work, we construct a wave-packet creation operator directly in the interacting theory to circumvent adiabatic evolution, taking advantage of resource-efficient schemes for ground-state preparation, such as variational quantum eigensolvers. By means of an ansatz for bound mesonic excitations in confining gauge theories, which is subsequently optimized using classical or quantum methods, we show that interacting mesonic wave packets can be created efficiently and accurately using digital quantum algorithms that we develop. Specifically, we obtain high-fidelity mesonic wave packets in the Z2 and U(1) lattice gauge theories coupled to fermionic matter in 1+1 dimensions. Our method is applicable to both perturbative and non-perturbative regimes of couplings. The wave-packet creation circuit for the case of the Z2 lattice gauge theory is built and implemented on the Quantinuum H1-1 trapped-ion quantum computer using 13 qubits and up to 308 entangling gates. The fidelities agree well with classical benchmark calculations after employing a simple symmetry-based noise-mitigation technique. This work serves as a step toward quantum computing scattering processes in quantum chromodynamics.

Presenter: Liam Jeanette, University of Maryland

Title: Blind Quantum Tomography on a Trapped-ion Quantum Computer

Abstract: We perform a method of quantum state tomography which simultaneously recovers the prepared quantum state, ρ, along with any measurement errors, ξ, that may have occurred during the measurement of ρ. We verify that the Blind Tomography method can recover a state and errors with high accuracy by performing Blind Tomography on a 3-qubit random product state prepared on a trapped-ion quantum computer with known amounts of error injected into the measurements. We show that the Blind Tomography method's success is independent of the magnitude of added errors, while standard tomography methods' performance degrades as errors are added. Finally, we show that the Blind Tomography method serves as an easy way to estimate the native errors present in our system and we compare the results to previous efforts for finding our native errors.

Presenter: Peiyi Li, NC State University

Title: QuTracer: Mitigating Quantum Gate and Measurement Errors by Tracing Subsets of Qubits 

Abstract: Quantum error mitigation plays a crucial role in the current noisy-intermediate-scale-quantum (NISQ) era. As we advance towards achieving a practical quantum advantage in the near term, error mitigation emerges as an indispensable component. One notable prior work, Jigsaw, demonstrates that measurement crosstalk errors can be effectively mitigated by measuring subsets of qubits. Jigsaw operates by running multiple copies of the original circuit, each time measuring only a subset of qubits. The localized distributions yielded from measurement subsetting suffer from less crosstalk and are then used to update the global distribution, thereby achieving improved output fidelity. Inspired by the idea of measurement subsetting, we propose QuTracer, a framework designed to mitigate both gate and measurement errors in subsets of qubits by tracing the states of qubit subsets throughout the computational process. In order to achieve this goal, we introduce a technique, qubit subsetting Pauli checks (QSPC), which utilizes circuit cutting and Pauli Check Sandwiching (PCS) to trace the qubit subsets distribution to mitigate errors. The QuTracer framework can be applied to various algorithms including, but not limited to, VQE, QAOA, quantum arithmetic circuits, QPE, and Hamiltonian simulations. In our experiments, we perform both noisy simulations and real device experiments to demonstrate that QuTracer is scalable and significantly outperforms the state-of-the-art approaches.

Presenter: Cheng-Ju Lin, University of Maryland

Title: Approximate quantum error correction from SU (2) irreducible representations

Abstract: We consider the irreducible representation of the total SU (2) rotation on N of spin-s. We show that a subset of the basis for the irreducible representation forms a covariant approximate quantum error correcting code. With the “thermodynamic code” as a special case of this class of codes, we show the code performance is essentially given by the algebraic relations of the basis of the SU (2) irreducible representation. This class of the code can host a probe state with a quantum Fisher information advantage beyond the standard quantum limit, when the sensing parameter is generated by the U (1) logical gate of the code. Using the code performance, we obtain a bound on the loss of the quantum Fisher information when the probe state goes through a noise channel. We numerically confirm our bound and that the probe state can retain its quantum advantage of quantum Fisher information in the presence of noise.

Presenter: Maryam Mudassar, University of Maryland

Title: Encoding Majorana codes

Abstract: A Majorana fermion a type of particle which is its own antiparticle. They can emerge as quasi- particles which are bound to defects in superconducting systems, and exist at zero energies, hence they are also known as Majorana zero modes or MZM’s. There are many theoretical predictions, as well as experimental developments in trying to find a Majorana fermion, but to date, the Majorana remains elusive. Majoranas are also interesting from a quantum information perspective because information can be encoded into non local degrees of freedom (such as into the edge states of a 1D Kitaev chain) and because of their non-Abelian exchange statistics, which allows one to do error robust gates in the form of braiding operations. Motivated by their potential, Majorana fermionic codes were initially introduced by Bravyi et al in [1] as extensions of the Kitaev chain, and inte- grates Majorana fermions into an error correcting code where qubits are encoded into the logical subspace of physical Majoranas, and thus these codes can protect against low weight fermionic noise. A distinct advantage of fermion based codes is that they admit a wider range of codes, since not all fermion codes can be mapped to bosonic codes. In order to run an error correction protocol on Majorana fermion codes, we first need a method to encode logical qubits in terms of physical fermions. In this paper, we use the so-called logical braid gates introduced in [2] to construct an algorithm that takes as input a general Majorana stabilizer code, and gives an encoding circuit, in terms of quadratic and quartic Majorana braid gates. We provide two approaches, one that uses an ancilla mode and works for any stabilizer code, while the second approach does not use an ancilla but does not work when the total parity is inside the stabilizer group. We hope this result will be useful in Majorana based platforms that use braiding operations to perform gates on Majorana modes.

Presenter: Greeshma Shivali Oruganti, University of Maryland

Title: Quantum Work and Heat during Sudden Quenches of Strongly Coupled Systems

Abstract: We present three frameworks for constructing thermodynamic quantities such as internal energy, free energy, entropy, work and heat for quantum systems strongly coupled to a reservoir. We consider three definitions of the system’s internal energy. For sudden quench processes, the proposed internal energy definitions imply corresponding definitions of work and heat that satisfy the first law of thermodynamics. We find that two of these frameworks additionally satisfy the second law of thermodynamics, while the third violates it. We illustrate our results using a simple spin-model.

Presenter: Joseph Ryan, Duke University

Title: Noise driven escape times in trapped ion systems

Abstract: Trapped atomic ions are a promising platform for large scale quantum computation. To date, one of their biggest drawbacks has been the effects of 'anomalous motional heating' caused by electric field noise associated with trap surfaces. Precise understanding of the underlying mechanisms remains elusive, and this is a problem of considerable interest since motional heating impacts the fidelity of coherent operations and the length of time during which they can be performed. In order to shed light on these processes, we carry out simulations of first passage time distributions (FPTDs) associated with ion heating in the highly underdamped limit. These FPTDs make it possible to distinguish between correlated 'multiplicative' or 'parametric forcing' noise, and uncorrelated 'additive' noise. At long times, we find that the first passage time distribution (i.e., the distribution of times taken for the ion to gain a certain kinetic energy starting from the same initial condition) displays exponential decay for additive noise, while the decay for multiplicative noise appears to have a more complex form. The focus is mostly on a classical model, but connections to quantum models and experimental realizations are also touched upon.

Presenter: Yue Shi, Princeton University

Title: Towards a Rydberg Quantum Simulator at Cryogenic Temperatures

Abstract: Rydberg atom tweezer arrays have emerged as a powerful platform for quantum simulation and computation. We present progress towards the construction of a cryogenic tweezer array for Cs-133. While previous cryogenic Rydberg setups have focused on obtaining low background gas pressures for allowing the assembly of large unit-filled arrays, our setup is specifically designed to obtain a low-temperature blackbody radiation environment. This will be  particularly beneficial for approaches for simulating quantum spin systems that rely on Rydberg dressing or circular Rydberg states by potentially increasing the lifetime of the samples by orders of magnitude. These approaches will allow us to expand the quantum simulation toolbox by exploring a wide variety of XYZ spin Hamiltonians over longer simulation times.

This work is funded by Brown Science Foundation.

Presenter: Ke Sun, Duke University

Title: Quantum Simulation of Spin-Boson Models with Structured Bath

Abstract: The spin-boson model, involving spins interacting with a bath of quantum harmonic oscillators, is a widely used representation of open quantum systems. Trapped ions present a natural platform for simulating the quantum dynamics of such models, thanks to the presence of both high quality internal qubit states and the motional modes of the ions that can simulate the relevant quantum degrees of freedom.  In our work, we extend the previous body of work that focused on coherent coupling of the spins and bosons to perform quantum simulations with structured dissipative baths using the motional states of trapped ions. We demonstrate the capability for adjusting the bath's temperature and continuous spectral density by adding randomness to fully programmable control parameters. Subsequently, we simulate the dynamics of various spin-boson models with noise spectral densities constructed from coupling to several dissipative harmonic oscillator modes. The experimental outcomes closely align with theoretical predictions, indicating successful simulation of open quantum systems using a trapped-ion system.

Presenters: Shiv Akshar Yadavalli and Iman Marvian, Duke University

Title: Optimal Distillation of Coherent States using Phase-insensitive Operations

Abstract: By combining multiple copies of thermal coherent states of light (or other bosonic systems), it is possible to obtain a single mode in thermal coherent state with a lower temperature, a process known as distillation or purification of coherent states. We investigate the distillation of coherent states under general phase-insensitive operations and find a distillation protocol that is optimal in the asymptotic regime, i.e., when the number of input copies is much greater than 1. Remarkably, we find that in this regime, the error -- as quantified by infidelity (one minus the fidelity) of the output state with the desired coherent state -- is proportional to the inverse of the purity of coherence of the input state, a quantity obtained from the Right-Logarithmic-Derivative (RLD) Fisher information metric, hence revealing an operational interpretation of this quantity. Our protocol is also optimal for converting a thermal coherent state to one with lower temperature and lower amplitude, in the regime where the output amplitude is significantly weaker than the input. While both the input and desired output are Gaussian states, we find that the optimal protocol cannot be a Gaussian channel. Among Gaussian phase-insensitive channels, the optimal distillation protocol is a simple linear optical scheme that can be implemented with beam splitters.

Presenter: Yuxuan Zhang, University of Maryland

Title: Crystalline Invariants of Integer and Fractional Chern Insulators

Abstract: The theory of topological phases of matter predicts a set of invariants protected by the crystalline symmetry. Here we show how to extract these many-body invariants {\Theta} in a concrete microscopic model (Hofstadter model) with non-zero Chern number C. We show that {\Theta} Together with C, chiral central charge c_ , and filling \nu provide a complete classification of the topological state with the crystalline symmetry group. Moreover, when the ground state has Abelian or Non-Abelian topological order, we can apply the same partial rotation method to calculate the full classification of the system. These invariants can be theoretically calculated through methods in conformal field theory, G-crossed braided tensor categories, and parton mean field theory, which remarkably agree with the numerical results.

TUESDAY 6/25/24:

Presenter: Trond Anderson, Google

Title: Thermalization and criticality on an analog-digital quantum simulator

Abstract: Understanding how interacting particles approach thermal equilibrium is a major goal of quantum simulation. Analog quantum simulators are appealing platforms for achieving this goal since they directly implement Hamiltonian dynamics, which are faster and less constrained by decoherence than in digital Trotter schemes. We here present a hybrid digital-analog quantum simulator comprising 69 superconducting qubits which exhibits very low analog evolution error and performance beyond the reach of classical simulation in cross-entropy benchmarking experiments. Simulating an XY quantum magnet, we observe clear signatures of the Kosterlitz-Thouless phase transition - including the emergence of algebraically decaying correlations with an exponent near the expected universal value of ¼ - as well as a consequent breakdown of Kibble-Zurek scaling. We substantiate our interpretations by tuning the energy density of the initial state, which enables studying the effects of the eigenstate thermalization hypothesis (ETH) in targeted parts of the energy spectrum. Lastly, we directly image thermalization and transport of energy by leveraging our hybrid capabilities to prepare the system in pairwise-entangled dimer states. These results establish the efficacy of superconducting analog-digital quantum processors for preparing states across many-body spectra and unveiling their thermalization dynamics.

Presenter: Peyman Azodi, Princeton University

Title: Decoherence time enhancement using particle destructive interference

Abstract: The persistence of effective light cones in long-range interacting quantum systems remains a notable and fascinating puzzle. Recently, we have demonstrated that this phenomenon is rooted in a purely quantum mechanical characteristic, specifically the destructive interference of quasi-particles, which are initially responsible for the system's thermalization. This destructive interference allows the system to avoid thermalization. Consequently, this phenomenon results in counter-intuitively slower thermalization rates when interactions are increased. Hence, a future research direction is to utilize such interactions to both (I) enhance computational efficiency and (II) reduce decoherence times. In this study, we identify the types of interactions that lead to the destructive interference phenomenon. Given that this phenomenon has already been experimentally simulated on various quantum computing platforms, this proposal could lead to a feasible and robust quantum computation strategy in the near future.

Presenter: Hossein Dehghani, University of Maryland

Title: Fault-tolerant hyperbolic Floquet quantum error correcting codes

Abstract: A central goal in quantum error correction is to reduce the overhead of fault-tolerant quantum computing by increasing noise thresholds and reducing the number of physical qubits required to sustain a logical qubit. We introduce a potential path towards this goal based on a family of dynamically generated quantum error correcting codes that we call "hyperbolic Floquet codes." These codes are defined by a specific sequence of non-commuting two-body measurements arranged periodically in time that stabilize a topological code on a hyperbolic manifold with negative curvature. We focus on a family of lattices for qubits that, according to our prescription that defines the code, provably achieve a finite encoding rate and have a depth-3 syndrome extraction circuit. Similar to hyperbolic surface codes, the distance of the code at each time-step scales at most logarithmically in . The family of lattices we choose indicates that this scaling is achievable in practice. We develop and benchmark an efficient matching-based decoder that provides evidence of a threshold near 0.1% in a phenomenological noise model. Utilizing weight-two check operators and a qubit connectivity of 3, one of our hyperbolic Floquet codes uses 400 physical qubits to encode 52 logical qubits with a code distance of 8, i.e., it is a code. At small error rates, comparable logical error suppression to this code requires 5x as many physical qubits (1924) when using the honeycomb Floquet code with the same noise model and decoder.

Presenter: Alaina Green, University of Maryland

Title: Molecular Cluster Design on a Quantum Computer

Abstract: Electronic excitation of molecular clusters are the microscopic dynamics governing the efficacy of both photovoltaic cells and photosynthetic reaction centers, as well as those emerging technologies that lie in between. In most cases, accurately capturing the behavior of such systems requires understanding not only the electronic excitations, but also the dynamics of the vibrational degrees of freedom, to which they are often coupled. Simulating the dynamics of such an expansive Hilbert space is a prime application of quantum computers. In this work, we experimentally simulate the transfer of an electronic excitation along a chain of macromolecules under a variety of conditions using a trapped-ion-based quantum computer. Our approach begins by using the relatively accessible spectroscopic data of an isolated macromolecule, pseudoisocyanine, as the input to a hybrid quantum-classical optimization algorithm which creates a digitally prepared wavefunction describing that macromolecule. Thereafter, we use an ab initio model to track the dynamics of a cluster of three macromolecules. We perform these simulations for a variety of different inter-molecular couplings by varying the relative angle between the molecules in the cluster, providing proof of principle for ab-initio design of molecular clusters with tailored excitation transfer rates.

Presenter: Navya Gupta, University of Maryland

Title: Euclidean Monte Carlo informed ground state preparation for quantum simulation

Abstract: Quantum simulators offer great potential for investigating the dynamical properties of quantum field theories. However, a key challenge is the preparation of high-fidelity initial states for these simulations. In this study, we focus on ground states and explore how information about their static properties, which can be efficiently obtained using classical methods such as path-integral Monte Carlo, can help identify suitable initial states. For the scalar field theory in 1+1 dimensions, we demonstrate variational ansatz families that yield comparable ground state energy estimates but exhibit distinct correlations and local non-Gaussianity. The simulation of quantum dynamics is expected to be highly sensitive to such initial state moments beyond the energy. We show that it is possible to optimize the behavior of selected ansatz moments using known ground state moments to address specific simulation needs. Drawing inspiration from the scalar field theory, our ultimate goal is to utilize existing lattice quantum chromodynamics (QCD) data to inform the preparation of the QCD ground state on quantum simulators.

Presenter: Hyunsoo Ha, Princeton University

Title: Measurement-induced phase transitions in systems with diffusive dynamics

Abstract: The competition between scrambling and projective measurements can lead to measurement-induced entanglement phase transitions (MIPT). In this work, we show that the universality class of the MIPT is drastically altered when the system is coupled to a diffusing conserved density. Specifically, we consider a 1+1d random Clifford circuit locally monitored by classically diffusing particles (``measurers''). The resulting diffusive correlations in the measurement density are a relevant perturbation to the usual space-time random MIPT critical point, producing a new universality class for this phase transition. We find ``Griffiths-like'' effects due to rare space-time regions where, e.g., the diffusive measurers have a low or high density, but these are considerably weaker than the Griffiths effects that occur with quenched randomness that produce rare spatial regions with infinite lifetime.

Presenter: Shubham Jain, University of Maryland

Title: Æ codes

Abstract: Diatomic molecular codes [arXiv:1911.00099] are designed to encode quantum information in the orientation of a diatomic molecule, allowing error correction from small torques and changes in angular momentum. Here, we directly study noise native to atomic and molecular platforms -- spontaneous emission, stray electromagnetic fields, and Raman scattering -- and show that diatomic molecular codes fail against this noise. We derive simple necessary and sufficient conditions for codes to protect against such noise. We also identify existing and develop new absorption-emission (Æ) codes that are more practical than molecular codes, require lower average momentum, can directly protect against photonic processes up to arbitrary order, and are applicable to a broader set of atomic and molecular systems.

Presenter: Qiang Miao, Duke University

Title: Equivalence of cost concentration and gradient vanishing for quantum circuits: An elementary proof in the Riemannian formulation

Abstract: The optimization of quantum circuits can be hampered by a decay of average gradient amplitudes with increasing system size. When the decay is exponential, this is called the barren plateau problem. Considering explicit circuit parametrizations (in terms of rotation angles), it has been shown in Arrasmith et al., Quantum Sci. Technol. 7, 045015 (2022) that barren plateaus are equivalent to an exponential decay of the cost-function variance. We show that the issue is particularly simple in the (parametrization-free) Riemannian formulation of such optimization problems and obtain a tighter bound for the cost-function variance. An elementary derivation shows that the single-gate variance of the cost function is strictly equal to half the variance of the Riemannian single-gate gradient, where we sample variable gates according to the uniform Haar measure. The total variances of the cost function and its gradient are then both bounded from above by the sum of single-gate variances and, conversely, bound single-gate variances from above. So, decays of gradients and cost- function variations go hand in hand, and barren plateau problems cannot be resolved by avoiding gradient-based in favor of gradient-free optimization methods.

Presenter: Matthew Molinelli, Princeton University

Title: Inductive coupling scheme for quantum simulation with superconducting qubits

Abstract: Superconducting qubits provide a promising platform for quantum simulation of Bose-Hubbard Hamiltonians due to the flexibility of tuning system parameters. Changing the ratio of on-site interaction strength due to qubit anharmonicity and coupling strength between qubits allows exploration of different quantum phases in the Bose-Hubbard model. Probing these quantum phase transitions requires the ability to dynamically tune the coupling strength. An inductive coupling scheme can make use of the nonlinearity of a Josephson junction to dynamically change the mutual inductance between two qubits by applying a DC magnetic flux [1]. The relative mutual inductances between the qubits and couplers can be engineered to achieve a large range of coupling strengths. Having both a high coupling strength and the ability to tune between positive and negative couplings enables quantum simulation experiments in various parameter regimes. We present our experimental realization and characterization of a tunable inductive coupler between transmon qubits.

Presenter: Sean Muleady, University of Maryland

Title: Quantum-enhanced sensing on an optical transition via finite-ranged interactions

Abstract: Control over quantum states in atomic systems has enabled the development of the most precise atomic clocks to date. Despite these advancements, demonstrating a quantum advantage in such systems remains challenging. One obstacle is that while finite-range interactions, such as dipolar, van der Waals, and far-detuned phonon-mediated interactions, are prevalent in current quantum platforms, generating entangled resources for quantum sensing applications—such as spin squeezing and GHZ states—typically requires infinite-range interactions. Here, we utilize chains of trapped ions to experimentally demonstrate that finite-range interactions can nevertheless be harnessed to generate collective dynamical behavior, enabling the production of metrologically useful entanglement. By leveraging interactions that decay as a power law function of the ion separation, we achieve spin squeezing at -3.9 dB below the standard quantum limit and create collective non-Gaussian states in the form of multi-headed cat states. These outcomes have immediate applications across various quantum sensing platforms that exhibit finite-range interactions, including arrays of ultracold atoms and molecules.

Presenter: Martin Ritter, University of Maryland

Title: Towards Experimental Realization of Topological Floquet Models in Circuit QED

Abstract: Topological band structures are well known to produce symmetry-protected chiral edge states which transport particles unidirectionally. These same effects can be harnessed in the frequency domain using a spin-1/2 system subject to periodic drives. Previously, the topological regime of such models was thought to be experimentally inaccessible due to a need for ultrastrong coupling; however, recent results have shown that the desired Hamiltonian is achievable in a rotating frame and can give rise to translations of non-classical states of light in a cavity in the Fock basis which we call "boosting". The native strong light-matter coupling in circuit QED along with tunable qubits allows us to tune the system into the regime where boosting can occur. Here I will present the design we have developed to achieve the strong driving necessary to reach the topological pumping regime and discuss our progress towards realizing boosting.

Presenter: Haohai Shi, University of Maryland

Title: "Super Atom" Encoding: An Analog Encoding Scheme for Positional Disorder Suppression on Rydberg Atom Arrays 

Abstract: The accuracy of analog quantum simulation on Rydberg atoms arrays is mainly limited by the uncertainty of each atom's position (the positional disorder). We introduce the "super atom" encoding scheme, which treats the collective behavior of several closely-placed Rydberg atoms equivalently as a simple "super atom" with two levels. By averaging the interaction over m copies of atoms, the encoding scheme reduces the error caused by positional disorder to ~$1/\sqrt{m}$ of the unencoded experiment.

Presenter: Grace Sommers, Princeton University

Title: Zero-temperature entanglement membranes in quantum circuits

Abstract: In chaotic quantum systems, the entanglement of a region A can be described in terms of the surface tension of a spacetime membrane pinned to the boundary of A. Here, we interpret the tension of this entanglement membrane in terms of the rate at which information “flows” across it. For any orientation of the membrane, one can define (generically nonunitary) dynamics across the membrane; we explore this dynamics in various space-time translation-invariant (STTI) stabilizer circuits in one and two spatial dimensions. We find that the flux of information across the membrane in these STTI circuits reaches a steady state. In the cases where this dynamics is nonunitary and the steady state flux is nonzero, this occurs because the dynamics across the membrane is unitary in a subspace of extensive entropy. This generalized unitarity is present in a broad class of STTI stabilizer circuits, and is also present in some special non-stabilizer models. The existence of multiple unitary (or generalized unitary) directions forces the entanglement membrane tension to be a piecewise linear function of the orientation of the membrane; in this respect, the entanglement membrane behaves like an interface in a zero-temperature classical lattice model. We argue that entanglement membranes in random stabilizer circuits that produce volume-law entanglement are also effectively at zero temperature.

Presenter: Yuxin Wang, University of Maryland

Title: Uncovering measurement-induced entanglement via feedforward

Abstract: The rich entanglement dynamics and transitions exhibited by monitored quantum systems typically only exist in the conditional state, making observation extremely difficult. Here, we present a general recipe for mimicking the conditional entanglement dynamics of a monitored system in a corresponding measurement-free dissipative system involving directional interactions between the original system and a set of auxiliary register modes. This mirror setup autonomously implements a measurement-feedforward dynamics that effectively retains a small fraction of the information content in a typical measurement record. We illustrate those ideas in a bosonic system featuring a competition between entangling measurements and local unitary dynamics, and also discuss extensions to qubit systems and truly many-body systems.

Presenter: Xiao Xiao, University of Maryland

Title: Finding optimal fault-tolerant circuits via satisfiability modulo theory

Abstract: Traditional fault tolerant schemes such as Shor, Steane, and Knill type error correction have large qubit overhead and there are efforts in reducing overhead with scheme such as adding flag qubits. To find the optimal circuit in terms of qubit count, circuit depth, and two-qubit gate count, we compactly encode the fault-tolerant constraints using the circuit to code mapping and find error correction conditions on the spacetime code that satisfy the fault-tolerant conditions for distance three codes. We are able to prove optimality of syndrome extraction and state preparation circuits via satisfiability modulo theory (SMT) solver for some small codes with a given gate set and show improvements on other protocols via Monte Carlo simulation.

Presenter: Jiayao Zhao, University of Maryland

Title: Exploring dynamics in Noisy Haar Random Circuits with Error Mitigation Techniques

Abstract: Error mitigation is pivotal for the advancement of near-term quantum computation. This poster presents an investigation of noisy Haar random circuits employing probabilistic error cancellation (PEC) and tensor network error mitigation (TEM) methods. By adopting the statistical mechanical mapping approach, the study translates Haar random circuits into the classical random field Ising model (RFIM). Utilizing a transition matrix that averages over the Haar measure, the research examines Rényi entropy and the linear cross-entropy benchmark (XEB) to study dynamics and characterize phase transitions relative to disorder strength. Matrix product states (MPS) are employed to represent probability distribution in two copy states, while the time-evolving block decimation (TEBD) algorithm facilitates the simulation of temporal evolution.