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1. Exact Results for a Boundary-Driven Double Spin Chain and Resource-Efficient Remote Entanglement Stabilization

   https://doi.org/10.1103/PhysRevX.14.021028  

   Lingenfelter, Andrew; Yao, Mingxing; Pocklington, Andrew; Wang, Yu-Xin; Irfan, Abdullah; Pfaff, Wolfgang; Clerk, Aashish A (May 2024, Physical Review X)

   We derive an exact solution for the steady state of a setup where two $XX$-coupled $N$-qubit spin chains (with possibly nonuniform couplings) are subject to boundary Rabi drives and common boundary loss generated by a waveguide (either bidirectional or unidirectional). For a wide range of parameters, this system has a pure entangled steady state, providing a means for stabilizing remote multiqubit entanglement without the use of squeezed light. Our solution also provides insights into a single boundary-driven dissipative $XX$spin chain that maps to an interacting fermionic model. The nonequilibrium steady state exhibits surprising correlation effects, including an emergent pairing of hole excitations that arises from dynamically constrained hopping. Our system could be implemented in a number of experimental platforms, including circuit QED. Published by the American Physical Society2024 

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2. Hidden Time Reversal in Driven $XXZ$ Spin Chains: Exact Solutions and New Dissipative Phase Transitions

   https://doi.org/10.1103/PhysRevLett.134.130404  

   Yao, Mingxing; Lingenfelter, Andrew; Belyansky, Ron; Roberts, David; Clerk, Aashish A (April 2025, Physical Review Letters)

   We show that several models of interacting $XXZ$spin chains subject to boundary driving and dissipation possess a subtle kind of time-reversal symmetry, making their steady states exactly solvable. We focus on a model with a coherent boundary drive, showing that it exhibits a unique continuous dissipative phase transition as a function of the boundary drive amplitude. This transition has no analog in the bulk closed system or in incoherently driven models. We also show the steady-state magnetization exhibits a surprising fractal dependence on interaction strength, something previously associated with less easily measured infinite-temperature transport quantities (the Drude weight). Our exact solution also directly yields driven-dissipative double-chain models that have pure, entangled steady states that are current carrying. Published by the American Physical Society2025 

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3. Efficiently Verifiable Quantum Advantage on Near-Term Analog Quantum Simulators

   https://doi.org/10.1103/PRXQuantum.6.010341  

   Liu, Zhenning; Devulapalli, Dhruv; Hangleiter, Dominik; Liu, Yi-Kai; Kollár, Alicia J; Gorshkov, Alexey V; Childs, Andrew M (March 2025, PRX Quantum)

   Existing schemes for demonstrating quantum computational advantage are subject to various practical restrictions, including the hardness of verification and challenges in experimental implementation. Meanwhile, analog quantum simulators have been realized in many experiments to study novel physics. In this work, we propose a quantum advantage protocol based on verification of an analog quantum simulation, in which the verifier need only run an $O\left({\lambda }^2\right)$-time classical computation, and the prover need only prepare $O\left(1\right)$samples of a history state and perform $O\left({\lambda }^2\right)$single-qubit measurements, for a security parameter $\lambda$. We also propose a near-term feasible strategy for honest provers and discuss potential experimental realizations. Published by the American Physical Society2025 

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4. Concomitant Entanglement and Control Criticality Driven by Collective Measurements

   https://doi.org/10.1103/PRXQuantum.6.010351  

   Iadecola, Thomas; Wilson, Justin H; Pixley, JH (March 2025, PRX Quantum)

   Adaptive quantum circuits—where a quantum many-body state is controlled using measurements and conditional unitary operations—are a powerful paradigm for state preparation and quantum error-correction tasks. They can support two types of nonequilibrium quantum phase transitions: measurement-induced transitions between volume- and area-law-entangled steady states and control-induced transitions where the system falls into an absorbing state or, more generally, an orbit visiting several absorbing states. Within this context, nonlocal conditional operations can alter the critical properties of the two transitions and the topology of the phase diagram. Here, we consider the scenario where the measurements are , in order to engineer efficient control onto dynamical trajectories. Motivated by Rydberg-atom arrays, we consider a locally constrained model with global sublattice magnetization measurements and local correction operations to steer the system’s dynamics onto a many-body orbit with finite recurrence time. The model has a well-defined classical limit, which we leverage to aid our analysis of the control transition. As a function of the density of local correction operations, we find control and entanglement transitions with continuously varying critical exponents. For sufficiently high densities of local correction operations, we find that both transitions acquire a dynamical critical exponent $z<1$, reminiscent of criticality in long-range power-law interacting systems. At low correction densities, we find that the criticality reverts to a short-range nature with $z\gtrsim 1$. In the long-range regime, the control and entanglement transitions are indistinguishable to within the resolution of our finite-size numerics, while in the short-range regime we find evidence that the transitions become distinct. We conjecture that the effective long-range criticality mediated by collective measurements is essential in driving the two transitions together. Published by the American Physical Society2025 

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5. Coherent Acoustic Control of Defect Orbital States in the Strong-Driving Limit

   https://doi.org/10.1103/PRXQuantum.5.030336  

   McCullian, BA; Sharma, V; Chen, HY; Crossman, JC; Mueller, EJ; Fuchs, GD (August 2024, PRX Quantum)

   We use a bulk acoustic wave resonator to demonstrate coherent control of the excited orbital states in a diamond nitrogen-vacancy ( $\text{N}$ $\mathrm{V}$) center at cryogenic temperature. Coherent quantum control is an essential tool for understanding and mitigating decoherence. Moreover, characterizing and controlling orbital states is a central challenge for quantum networking, where optical coherence is tied to orbital coherence. We study resonant multiphonon orbital Rabi oscillations in both the frequency and time domain, extracting the strength of the orbital-phonon interactions and the coherence of the acoustically driven orbital states. We reach the strong-driving limit, where the physics is dominated by the coupling induced by the acoustic waves. We find agreement between our measurements, quantum master-equation simulations, and a Landau-Zener transition model in the strong-driving limit. Using perturbation theory, we derive an expression for the orbital Rabi frequency versus the acoustic drive strength that is nonperturbative in the drive strength and agrees well with our measurements for all acoustic powers. Motivated by continuous-wave spin-resonance-based decoherence protection schemes, we model the orbital decoherence and find good agreement between our model and our measured few-to-several-nanoseconds orbital decoherence times. We discuss the outlook for orbital decoherence protection. Published by the American Physical Society2024 

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