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1. Experimental Realization of Discrete Time Quasicrystals

   https://doi.org/10.1103/physrevx.15.011055  

   He, Guanghui; Ye, Bingtian; Gong, Ruotian; Yao, Changyu; Liu, Zhongyuan; Murch, Kater W; Yao, Norman Y; Zu, Chong (March 2025, Physical Review X)

   Floquet (periodically driven) systems can give rise to unique nonequilibrium phases of matter without equilibrium analogs. The most prominent example is the realization of discrete time crystals. An intriguing question emerges: What other novel phases can manifest when the constraint of time periodicity is relaxed? In this study, we explore quantum systems subjected to a quasiperiodic drive. Leveraging a strongly interacting spin ensemble in diamond, we identify the emergence of long-lived discrete time quasicrystals. Unlike conventional time crystals, time quasicrystals exhibit robust subharmonic responses at multiple incommensurate frequencies. Furthermore, we show that the multifrequency nature of the quasiperiodic drive allows for the formation of diverse patterns associated with different discrete time quasicrystalline phases. Our findings demonstrate the existence of nonequilibrium phases in quasi-Floquet settings, significantly broadening the catalog of novel phenomena in driven many-body quantum systems. Published by the American Physical Society2025 

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2. Mesoscale field theory for quasicrystals

   https://doi.org/10.1103/PhysRevResearch.6.043285  

   De_Donno, Marcello; Angheluta, Luiza; Elder, Ken R; Salvalaglio, Marco (December 2024, Physical Review Research)

   We present a mesoscale field theory unifying the modeling of growth, elasticity, and dislocations in quasicrystals. The theory is based on the amplitudes entering their density-wave representation. We introduce a free energy functional for complex amplitudes and assume nonconserved dissipative dynamics to describe their evolution. Elasticity, including phononic and phasonic deformations, along with defect nucleation and motion, emerges self-consistently by prescribing only the symmetry of quasicrystals. Predictions on the formation of semicoherent interfaces and dislocation kinematics are given. Published by the American Physical Society2024 

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3. Stabilizing steady-state properties of open quantum systems with parameter engineering

   https://doi.org/10.1103/PhysRevResearch.7.023057  

   Aydoğan, Koray; Schlimgen, Anthony W; Head-Marsden, Kade (April 2025, Physical Review Research)

   Realistic quantum systems are affected by environmental loss, which is often seen as detrimental for applications in quantum technologies. Alternatively, weak coupling to an environment can aid in stabilizing highly entangled and mixed states, but determining optimal system-environment parameters can be challenging. Here, we describe a technique to optimize parameters for generating desired nonequilibrium steady states (NESSs) in driven-dissipative quantum systems governed by the Lindblad equation. We apply this approach to predict highly entangled and mixed NESSs in Ising, Kitaev, and Dicke models in several quantum phases. Published by the American Physical Society2025 

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4. Pattern formation in odd viscoelastic fluids

   https://doi.org/10.1103/PhysRevResearch.6.033100  

   Floyd, Carlos; Dinner, Aaron R; Vaikuntanathan, Suriyanarayanan (July 2024, Physical Review Research)

   Nonreciprocal interactions fueled by local energy consumption can be found in biological and synthetic active matter at scales where viscoelastic forces are important. Such systems can be described by “odd” viscoelasticity, which assumes fewer material symmetries than traditional theories. Here we study odd viscoelasticity analytically and using lattice Boltzmann simulations. We identify a pattern-forming instability which produces an oscillating array of fluid vortices, and we elucidate which features govern the growth rate, wavelength, and saturation of the vortices. Our observation of pattern formation through odd mechanical response can inform models of biological patterning and guide engineering of odd dynamics in soft active matter systems. Published by the American Physical Society2024 

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5. 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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