Materials Science · Cross-listed from quant-ph
Quantifying surface losses in superconducting aluminum microwave resonators
Elizabeth Hedrick, Faranak Bahrami, Alexander C. Pakpour-Tabrizi et al. (+11 more)
The recent realization of millisecond-scale coherence with tantalum-on-silicon transmon
qubits showed that depositing the Al/AlOx/Al Josephson junction in a high purity, ultrahigh
vacuum environment was critical for achieving lifetime-limited coherence, motivating careful examination of the aluminum surface two-level system (TLS) bath. Here, we measure the microwave absorption arising from surface TLSs in superconducting aluminum resonators, following methodology developed for tantalum resonators. We vary film and surface properties and correlate microwave measurements with materials characterization. We find that the lifetimes of superconducting aluminum resonators are primarily limited by surface losses associated with TLSs in the 2.7 nm-thick native AlOx. Treatment with 49% HF removes surface AlOx completely; however, rapid
oxide regrowth limits improvements in surface loss and long term device stability. Using these measurements we estimate that TLSs in aluminum interfaces contribute around 27% of the relaxation rate of state-of-the-art tantalum-on-silicon
qubits that incorporate aluminum-based Josephson junctions.
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All authors Elizabeth Hedrick, Faranak Bahrami, Alexander C. Pakpour-Tabrizi, Atharv Joshi, Q. Rumman Rahman, Ambrose Yang, Ray D. Chang, Matthew P. Bland, Apoorv Jindal, Guangming Cheng, Nan Yao, Robert J. Cava, Andrew A. Houck, Nathalie P. de Leon
Materials Science · Cross-listed from quant-ph
Beta Tantalum Transmon Qubits with Quality Factors Approaching 10 Million
Atharv Joshi, Apoorv Jindal, Paal H. Prestegaard et al. (+9 more)
Tantalum-based transmon
qubits are a promising platform for building large-scale
quantum processors. So far, these
qubits have been made from tantalum films grown exclusively in the alpha phase ({\alpha}-Ta). The beta phase of tantalum (\{beta}-Ta) readily nucleates at room temperature, making it attractive for scalable
qubit fabrication. However, \{beta}-Ta is widely believed to be detrimental to
qubit performance because it has a lower superconducting critical temperature than {\alpha}-Ta. We challenge this prevailing belief by fabricating low-loss transmon
qubits from \{beta}-Ta films on sapphire. Across 11
qubits, the mean time-averaged quality factor is (5.6 +/- 2.3) x 10^6, with the best
qubit recording a time-averaged quality factor of (10.1 +/- 1.3) x 10^6. Resonator studies demonstrate that the dominant microwave loss channel is surface two-level systems, with the surface loss contribution for \{beta}-Ta being about twice that of {\alpha}-Ta. \{beta}-Ta films exhibit significant kinetic inductance, consistent with an estimated
magnetic penetration depth of (1.78 +/- 0.02) {\mu}m. This work establishes \{beta}-Ta on sapphire as a material platform for realizing low-loss transmon
qubits and other superconducting devices such as compact resonators, kinetic inductance detectors, and quasiparticle traps.
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All authors Atharv Joshi, Apoorv Jindal, Paal H. Prestegaard, Faranak Bahrami, Elizabeth Hedrick, Matthew P. Bland, Tunmay Gerg, Guangming Cheng, Nan Yao, Robert J. Cava, Andrew A. Houck, Nathalie P. de Leon
Materials Science
Zinc selenide single crystals co-doped with active TM-ions of chromium, cobalt and iron
Sergei Naydenov, Oleksii Kapustnyk, Igor Pritula et al. (+1 more)
The development of
laser materials with absorption/emission spectra in the atmospheric transparency band 2-5 microns is of great interest for modern applications. Triple-doped zinc selenide
crystals activated with chromium, cobalt, and iron ions were grown by the vertical Bridgman method under high argon pressure. Comparative X-ray diffractometry, infra-red spectroscopy, and other studies of grown
crystals were conducted. Features of their growth, morphology, and optical properties related to the
crystal structure were discovered.
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All authors Sergei Naydenov, Oleksii Kapustnyk, Igor Pritula, Dmitro Sofronov
Statistical Mechanics
Towers of quantum many-body scars under stochastic resetting
Lorenzo Gotta, Manas Kulkarni and Gabriele Perfetto
Towers of
quantum many-body scars are sets of highly-excited eigenstates of nonintegrable
Hamiltonians whose dynamics shows athermal behavior and persistent oscillations in time. The preparation of such states is, however, challenging due to their
entanglement content. In this work, we show that local properties of such states can be prepared by interspersing the scarred dynamics with
stochastic resets to much simpler unentangled product states.
Stochastic resetting amounts to reinitializing the many-body wavefunction of the system at random times to a predefined state, which we choose to be in the scarred subspace. We derive several analytical results for the ensuing dynamics, e.g., for the time
evolution of the fidelity and of local observables. Resetting damps the scarred oscillations and generates spatial off-diagonal long-range order in the ensuing stationary state. The latter shows mixedness that scales logarithmically as a function of the system size, which follows from the structure of the scarred eigenstates. We prove that such stationary states are locally equivalent, in the sparse-resetting limit, to a single pure scarred eigenstate, which is determined by the reset state. This protocol thereby might represent a route to the experimental preparation of the local properties of correlated and entangled states through resetting.
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Disordered Systems and Neural Networks · Cross-listed from math.PR
Clustering without geometry in sparse networks with independent edges
Alessio Catanzaro, Remco van der Hofstad and Diego Garlaschelli
The coexistence of sparsity and clustering (non-vanishing average fraction of triangles per node) is one of the few structural features that, irrespective of finer details, are ubiquitously observed across large real-world networks. This fact calls for generic models producing sparse clustered graphs. Earlier results suggested that sparse random graphs with independent edges fail to reproduce clustering, unless edge probabilities are assumed to depend on underlying metric distances that, thanks to the triangle inequality, naturally favour triadic closure. This observation has opened a debate on whether clustering implies (latent) geometry in real-world networks. Alternatively, recent models of higher-order networks can replicate clustering by abandoning edge independence. In this paper, we mathematically prove, and numerically confirm, that a sparse random graph with independent edges, recently identified in the context of network renormalization as an invariant model under node aggregation, produces finite clustering without any
geometric or higher-order constraint. The underlying mechanism is an infinite-mean node fitness, which also implies a power-law degree distribution. Further, as a novel phenomenon that we characterize rigorously, we observe the breakdown of self-averaging of various network properties. Therefore, as an alternative to geometry or higher-order dependencies, node aggregation invariance emerges as a basic route to realistic network properties.
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Mesoscale and Nanoscale Physics
Nested Feature Spectrum Topology: Tripartite Topological Equivalence of Feature, Entanglement, and Wilson Loop Spectrum
Yi-Chun Hung, T. Tzen Ong and Hsin Lin
Topological phases of matter are traditionally characterized through
symmetry-based classifications. In cases of
symmetry breaking, the projected spectrum - obtained by projecting the ground state onto the eigenstates of a pertinent
quantum observable, such as
spin or orbital angular momentum - provides a clear method for classifying topological phases. This approach underpins well-known frameworks such as
spin-resolved
topology and feature spectrum
topology. Here we introduce nested feature spectrum
topology, in which projection operators are applied recursively to subsectors of the feature spectrum, generating a hierarchy of feature spectra. We uncover a fundamental tripartite equivalence among the
topology of feature, the
entanglement, and the Wilson loop spectra in non-interacting fermionic systems. This equivalence reveals that the feature spectrum encodes the
entanglement between sectors of the
quantum observable, such as the
spin-up and
spin-down states in
spin-resolved
topology. We further prove that spectral flow in the
entanglement spectrum and the Wilson loop winding in the feature spectrum are equivalent manifestations of the feature-energy complementarity: the appearance of gapless spectral flow in either energy or projected spectra on the boundary. This complementarity refines the conventional bulk-boundary correspondence by demonstrating that topological boundary modes may persist in the feature spectrum even when energy spectra are gapped. Our results provide a deeper understanding and solid foundation for the origin of band
topology in the feature spectrum.
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Statistical Mechanics
Out-of-equilibrium percolation transitions at finite critical times after quenches across magnetic first-order transitions
Andrea Pelissetto, Davide Rossini and Ettore Vicari
We show that an out-of-
equilibrium percolation transition occurs after quenching
ferromagnetic Ising-like systems across their
magnetic first-order transitions. As a paradigmatic example, we consider a two-dimensional Ising system driven across its low-temperature first-order transition line by a quench of the
magnetic field $h$ from $h_i<0$ to $h>0$. In the thermodynamic limit and for finite values of $h$, the post-quench
evolution under a purely relaxational dynamics is characterized by a dynamic transition at a finite critical time $t_c(h)$ from the metastable negatively magnetized phase to the positive one, marked by the percolation of the largest clusters of positive and negative
spins. This out-of-
equilibrium percolation transition displays a finite-size scaling behavior as in the standard random-percolation case. However, while the fractal dimension of the percolating clusters is consistent with the random-percolation value, the exponent controlling the approach to criticality differs and depends on $h$. We also show that the percolation critical behavior is related to the spinodal-like behavior of the magnetization in the small-$h$ limit, which implies that the percolation time $t_c(h)$ exhibits a spinodal-like exponential dependence on $h$.
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Statistical Mechanics · Cross-listed from quant-ph
Universal monitored dynamics in multimode bosonic systems
Shivam Patel, Catherine McCarthy, Ahana Chakraborty et al. (+5 more)
We propose a route to study monitored many-body dynamics in multimode bosonic systems using
circuit quantum electrodynamics. In this experimental setting, we construct several bosonic models comprising brickwork
circuits built from beam-splitter gates, local parity measurements, and optional on-site Hubbard interactions, and diagnose their monitored dynamics via ancilla purification and a learnability-based probe. Under parity measurements, generic gate sets exhibit behavior that is largely consistent with a conventional measurement-induced phase transition, while a special class of beam-splitter
circuits shows an apparent critical-like high-measurement regime in which purification times scale linearly with system size. We show that for realistic noise, gate, and measurement rates, these signatures are observable with near-term
circuit QED hardware.
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All authors Shivam Patel, Catherine McCarthy, Ahana Chakraborty, Jordan Huang, Thomas J. DiNapoli, Romain Vasseur, J. H. Pixley, Srivatsan Chakram
Materials Science
Rate-Dependent Reversibility and Lithium Losses in Hybrid Anode-Collector Metal Electrodes
Arturo Galindo, Jesus Diaz-Sanchez, Sunil Kumar et al. (+5 more)
Understanding how practical lithium storage capacity varies with charge-discharge rate is crucial for designing durable anode free lithium batteries. We examine the lithiation behavior of single element metal electrodes-Al (alloying), Mg (solid solution intercalation), Ag (solid solution then alloying), and Cu (surface Li plating)-to determine how their mechanisms influence reversibility, measured by coulombic efficiency. Using electrochemistry combined with depth resolved ion beam profiling, we map local coulombic efficiency across current densities and identify dominant lithium loss pathways. Ag uniquely sustains fast kinetics and high reversibility at elevated rates due to rapid formation of gamma brass-type
alloy phases. In contrast, Mg and Al show increasing irreversibility from kinetically or structurally driven Li trapping, while Cu exhibits the largest losses through porous, highly reactive plated lithium. These results reveal fundamental limits of anode free systems that depend on reversible Li plating without excess lithium and underscore the importance of metal selection for stable, high rate performance.
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All authors Arturo Galindo, Jesus Diaz-Sanchez, Sunil Kumar, Bouthayna Alrifai, Andrea Marchetti, Gaston Garcia, Celia Polop, Enrique Vasco
Superconductivity · Cross-listed from quant-ph
Experimental realization of a $\cos(2\varphi)$ transmon qubit
Erwan Roverc'h, Alvise Borgognoni, Marius Villiers et al. (+7 more)
Superconducting
circuits with embedded
symmetries are good candidates to robustly protect
quantum information from dominant error channels. The $\cos(2\varphi)$
qubit, consisting of an island shunted to ground through a tunneling element that selectively transmits pairs of Cooper pairs, leverages charge-parity
symmetry to protect from charge-induced errors. In this experiment, we observe a doublet of states of opposite Cooper-pair parity split by $13.6~\mathrm{MHz}$. Operating in a soft-transmon regime, this splitting is two orders of magnitude smaller than in previous implementations, pushing charge-induced losses well beyond the measured coherence times. Despite the low transition frequency, we demonstrate coherent
qubit control, single-shot readout, and resolve
quantum jumps. Charge protection of the
qubit is evidenced by a $100-$fold suppression of the island charge
matrix element compared to the unprotected plasmon transition, placing dielectric loss limits above $10~\mathrm{ms}$. The measured $T_1 = 70~\mu\mathrm{s}$ and $T_2^\mathrm{echo}= 2.5~\mu\mathrm{s}$ are instead limited by $1/f$ flux noise in the tunnelling element's loop. This experiment shows that pushing Cooper-pair pairing in the transmon regime sets high limits on charge-induced losses while preserving coherent control and single-shot readout of the low-frequency
qubit. We identify flux noise as the dominant remaining limitation, calling for gradiometric designs or novel $4e$-tunneling elements.
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All authors Erwan Roverc'h, Alvise Borgognoni, Marius Villiers, Kyrylo Gerashchenko, W. Clarke Smith, Christopher Wilson, Benoit Douçot, Alexandru Petrescu, Philippe Campagne-Ibarcq, Zaki Leghtas
Strongly Correlated Electrons
Putative quantum critical point in locally noncentrosymmetric CeCoGe$_2$ crystals
F. Garmroudi, C. S. T. Kengle, M. H. Schenck et al. (+4 more)
Locally noncentrosymmetric heavy-
fermion compounds may produce long-sought correlated
quantum phases, such as
spin-triplet superconductivity with non-Abelian quasiparticles, but identifying the right candidate systems is challenging. Here, using the In flux method, we synthesize CeCoGe$_2$ single
crystals, belonging to the highly tunable pseudotetragonal ($Cmcm$) Ce$TX_2$ family, which allows for substitutions at both the transition metal $T$ and at the $X$ sites. We identify a heavy-
fermion ground state with a Sommerfeld coefficient $\gamma\approx 120$ mJ mol$^{-1}$ K$^{-2}$ and a non-
Fermi-
liquid exponent of the electrical resistivity, which may indicate its proximity to the putative
quantum critical point. However, no signs of superconductivity or
magnetic order are detected down to 20 mK. Our analysis of electrical transport and structural properties indicates that coherent charge transport and the emergence of superconductivity observed under hydrostatic pressure in related compounds (CePtSi$_2$ and CeRhGe$_2$) are suppressed in CeCoGe$_2$ by strong random potential scattering due to intrinsic Co vacancies (approximately 4% even in the highest-quality
crystals). By tuning the growth stoichiometry and temperature profile, we demonstrate that the defect concentration can be controlled and has a pronounced effect on the residual resistivity. We hypothesize that superconductivity may be found in higher-quality CeCoGe$_2$
crystals grown by different techniques.
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All authors F. Garmroudi, C. S. T. Kengle, M. H. Schenck, J. D. Thompson, E. D. Bauer, S. M. Thomas, P. F. S. Rosa
Mesoscale and Nanoscale Physics
Band offsets in InP/ZnSe nanocrystals evaluated using two-photon transitions analysis
K.I. Russkikh, A.A. Golovatenko and A.V. Rodina
We present a semi-analytical theoretical kp-study of the energy structure and optical transitions in spherical core-shell InP/ZnSe nanocrystals. We use the eight-band Kane model and the six-band Luttinger
Hamiltonian in the spherical approximation to calculate the electron and hole energy spectra, respectively. The influence of the Coulomb interaction is considered perturbatively. The one- and two-
photon absorption spectra are calculated as functions of the band offsets between the InP core and ZnSe shell.
Exciton states responsible for the main features in the two-
photon absorption spectra of InP/ZnSe nanocrystals are identified and the spectral dependence of the linear-circular dichroism signal is predicted. We show that in the presence of inhomogeneous broadening, the transition to the ground two-
photon-active
exciton state can be hidden behind intense transitions to higher-lying states. A comparison of the calculated one- and two-
photon absorption spectra with the available experimental data shows that, depending on the
lattice strain in the InP core, the range of possible valence band offsets is 0.85-1 eV. The determined range exceeds the natural valence band offset of 0.57 eV and indicates the presence of electric dipoles formed by the preferential Zn-P bonds at the InP/ZnSe heterointerface.
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Strongly Correlated Electrons
SU(2) gauge theory of fluctuating stripe order in the two-dimensional Hubbard model
Henrik Müller-Groeling, Pietro M. Bonetti, Paulo Forni et al. (+1 more)
We present an SU(2) gauge theory of fluctuating stripe order in the two-dimensional Hubbard model. The theory is based on a fractionalization of the electron operators in fermionic chargons with a pseudospin degree of freedom, and charge neutral spinons capturing fluctuations of the
spin orientation. The chargons are treated in a renormalized mean-field theory. We focus on regions of the phase diagram where they undergo stripe order. The spinons are described by a non-linear sigma model with pseudospin stiffnesses determined by the chargons. They prevent breaking of the physical SU(2)
spin symmetry at any finite temperature, resulting in a charge ordered pseudogap phase with a reconstructed
Fermi surface and a
spin gap. The spectral function for single-particle excitations exhibits a collection of
Fermi arcs and other structures. The arcs appear in various regions of the Brillouin zone, but never exclusively around the Brillouin zone diagonals.
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All authors Henrik Müller-Groeling, Pietro M. Bonetti, Paulo Forni, Walter Metzner
Strongly Correlated Electrons
Data-efficient surrogate modeling of spectral functions using Gaussian processes: An application to the $t$-$t'$-$t''$-$J$ model
Sanket Jantre, Nathan M. Urban, Weiguo Yin et al. (+1 more)
Spectral functions encode key many-body information but are costly to compute with high fidelity. Machine-learning surrogates have emerged as a powerful alternative, yet many approaches require large training
datasets. We develop a data-efficient surrogate for spectral functions using the $t$-$t'$-$t''$-$J$ model, which describes the motion of a hole in a
quantum antiferromagnet. Using $\sim$ 10$^5$ self-consistent Born approximation-based spectra from Lee, Carbone and Yin (Phys. Rev. B 107, 205132 (2023)), we train a deep-kernel Gaussian process surrogate model with sparse variational inference (DKL-SVGP) using only 10% of the available training spectra. We
benchmark against feed-forward neural networks (FFNN) trained on the same reduced subset and on the full
dataset. The proposed DKL-SVGP model consistently outperforms the reduced-data FFNN and, despite using only 10% of the training spectra, achieves spectrum-wise errors within the same order-of-magnitude as the full-data FFNN baseline. Worst-tail diagnostics show improved fidelity on difficult spectra, while peak-level analysis indicates that DKL-SVGP recovers dominant peak heights with comparable accuracy and improves peak-location agreement under a matched-peak evaluation that mitigates rare peak-swapping cases. Overall, these results highlight GP-based surrogates as a competitive and data-efficient approach for spectral-function prediction in scarce-data regimes.
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All authors Sanket Jantre, Nathan M. Urban, Weiguo Yin, Niraj Aryal
Mesoscale and Nanoscale Physics
Topological electric field-defined quantum dots in bilayer graphene: An atomistic approach
Wlodzimierz Jaskolski
We study topological bound states in
quantum dots defined by an electric field in
bilayer graphene. An external field is perpendicular to the
bilayer and changes sign in a finite region that defines the
quantum dot. The electric field opens a gap in the
bilayer graphene, and the reversed field creates a domain wall with one-dimensional
chiral gapless bands localized therein. The finite size of dots leads to the quantization of these bands and the appearance of discrete bound states localized at the dot boundary. We consider rectangular dots oriented along the armchair and zigzag directions. We go beyond a simple continuum one-valley model and use an atomistic tight-binding approach. This allows us to identify new effects related to the atomic structure of
graphene, strengths of the electric field, valley mixing, and valley asymmetry.
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Mesoscale and Nanoscale Physics
Fast Nuclear Spin Read-Out in Single Molecule Magnets
Hongyan Chen, Simon Gerber, Philip Schmid et al. (+6 more)
Nuclear spins in 4f single-molecule magnets (SMMs) are promising
qubits or qudits candidates for
quantum information processing due to their relative isolation and reduced susceptibility to environmental disturbances, while their hyperfine coupling to the 4f
magnetic moments enable readout and control. So far, the
nuclear spin states of individual TbPc2 SMMs have been detected in transport measurements via the
spin-cascade effect. Here, we demonstrate a fast, field-sweep-free readout of
nuclear spin in individual 163DyPc2 (I = 5/2) and 159TbPc2 (I = 3/2) using millikelvin
spin-polarized scanning tunneling microscopy. This fast readout is enabled by the hyperfine interactions, which modifies the statistics of the telegraph noise generated by reversals of the Ln3+ moment, thereby revealing the
nuclear spin state. We observe
nuclear spin relaxation times T1 in excess of minutes. Furthermore, we drive
nuclear spin transitions using a
radio-frequency field and detect the resulting
nuclear magnetic resonance directly in the tunneling current. Thus our approach enables fast access to long-lived
nuclear spin states in an individual molecule
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All authors Hongyan Chen, Simon Gerber, Philip Schmid, Nola Warwick, Charanpreet Singh, Svetlana Klyatskaya, Eufemio Moreno-Pineda, Mario Ruben, Wulf Wulfhekel
Materials Science · Cross-listed from nlin.PS
Transition Waves for Energy Trapping and Harvesting
Sneha Srikanth and Andres F. Arrieta
The presence of multiple stable states and associated nonlinear phenomena, such as hysteresis, in multistable mechanical metamaterials enables frequency-independent energy harvesting and shock absorption. This study focuses on shock absorption achieved by locking transition waves to trap energy at designed locations within a multistable metamaterial. We further demonstrate that the same system can simultaneously harvest energy from impact loading, thereby exhibiting multifunctionality. The model of the multistable metamaterial is a one-dimensional chain of bistable units whose transition wave dynamics are related to topological solitary waves governed by the $\phi^4$ equation. This connection enables analytical estimation of critical design parameters required for energy trapping and also the amount of energy trapped. Numerical simulations and experiments show that trapping energy in transition waves leads to enhanced damping performance compared to corresponding linear metamaterials. We further propose design variations to increase the amount of energy trapped in the transition wave. Additionally, we identify energy splitting as a damping mechanism that arises when there are repeated impulses or a single high-amplitude impulse that generates multiple transition waves. The transition waves interact to produce localized, fast-dissipating breathers, leading to a damped response. Furthermore, experiments demonstrate that multistable metamaterials can simultaneously achieve improved energy harvesting and better damping performance compared to their linear counterparts. Together, these results highlight the use of transition waves for creating multifunctional multistable metamaterials.
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Mesoscale and Nanoscale Physics
Extending Topological Bound on Quantum Weight Beyond Symmetry-Protected Topological Phases
Yi-Chun Hung, Yugo Onishi, Hsin Lin et al. (+2 more)
The
quantum metric encodes the
geometric structure of Bloch wave functions and governs a wide range of physical responses. Its Brillouin-zone integral, the
quantum weight, appears in the structure factor and provides lower bounds on observables such as the optical gap and dielectric constant. In
symmetry-protected topological (SPT) phases, the nontrivial band
topology imposes a lower bound on the
quantum weight and constraints on the observables. Here, we generalize the topological bound on
quantum geometry to encompass systems beyond the SPT phases. We show that topological invariants defined via the projected spectrum lower-bound the
quantum weight with a
symmetry-breaking correction to the
quantum metric. Our proposed bound holds even when the underlying
symmetries are broken, and it would be amenable to experimental verification via the optical conductivity sum rule under external fields. We illustrate our theory by adding a nonzero
spin-orbit coupling term to a
spin Chern
insulator model, where we show that our proposed bound applies even though the conventional topological bound does not hold.
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All authors Yi-Chun Hung, Yugo Onishi, Hsin Lin, Liang Fu, Arun Bansil
Mesoscale and Nanoscale Physics
Imaging the high-frequency charging dynamics of a single impurity in a semiconductor on the atomic scale
Maialen Ortego Larrazabal, Jiasen Niu, Stephen R. McMillan et al. (+4 more)
As electronic devices approach the atomic limit, the charge dynamics of individual dopant atoms increasingly constrain performance, stability, and coherence. In scanning tunnelling microscopy (STM), donor ionization is typically interpreted as a static threshold process arising from tip-induced band bending. Here we show that the ionization of individual sulfur donors in InAs is intrinsically dynamic and governed by the local electric field. Using MHz-frequency STM noise spectroscopy with atomic-scale spatial mapping, we resolve pronounced random telegraph noise that is invisible in time-averaged tunnelling spectra. A bias-dependent model quantitatively links the noise spectra to microscopic ionization and neutralization processes of the donor states, enabling direct extraction of nanosecond charge-state lifetimes. The switching rate is strongly bias dependent, demonstrating that the electric field continuously drives charge-state transitions. Unexpectedly, we show that the degenerately doped bulk leads to a sharp bias-dependent onset of donor ionization as the donor level crosses the
Fermi level, giving rise to a characteristic shoulder in the noise power spectrum that is captured by our model. These results establish donor ionization as a non-
equilibrium dynamical process with nontrivial contribution by the bulk electrons, and identify
impurity switching as a universal nanoscale charge-noise mechanism relevant to
quantum devices.
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All authors Maialen Ortego Larrazabal, Jiasen Niu, Stephen R. McMillan, Paul M. Koenraad, Michael E. Flatté, Milan P. Allan, Ingmar Swart
Mesoscale and Nanoscale Physics
Noise-protected two-qubit gate using anisotropic exchange interaction
Zizheng Wu and Maximilian Rimbach-Russ
Hole
spin qubits hosted in Germanium
quantum dots are promising candidates for scalable
quantum computing. The strong
spin-orbit interaction can enable fast and all-electrical
quantum control. Furthermore, the platform can implement universal
quantum control using only baseband signals, which may mitigate the impact of crosstalk and microwave-induced heating. At the same time,
spin-orbit interaction gives rise to an anisotropic exchange interaction, whose potential for implementing two-
qubit gates has remained largely unexplored. However, the current performance of operating a hole-based
quantum computer is mostly limited by dephasing due to low-frequency charge noise. In this work, we propose a novel two-
qubit gate protocol for Germanium hole
spin qubits operated in the gapless regime. This gate protocol exploits the anisotropic exchange interaction between neighboring
spins and utilizes a composite pulse scheme implemented solely through electrical baseband signals. Using this approach, we predict high-fidelity two-
qubit controlled-Z operations that can suppress exchange-energy fluctuations, offering a pathway toward fault-tolerant
semiconductor quantum processors.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
Dipolar solvent contributions for transient nanoscale electroosmotic flow
Pramodt Srinivasula
Electrohydrodynamic flows of electrolytes with low to moderate ion concentration at the nanoscale are significantly influenced by the molecular structure of water-like polar solvents within the electric double layer (EDL). Moreover, unlike in microfluidics, at these length scales the time scale of
evolution of EDL often becomes comparable to the consequent fluidic phenomena of interest. While continuum descriptions to model such phenomena typically assume a constant dielectric and viscous solvent background, this study incorporates dipolar solvent physics. Specifically, both dielectric saturation and the viscoelectric effect are implemented together into a Poisson-Nernst-Planck-Stokes framework, using the Langevin-Bikerman solvent permittivity distribution and empirical viscoelectric coefficients, respectively. Numerical simulations in a one-dimensional geometry reveal substantial modifications to the electrohydrodynamic body force density and transient electroosmotic mobility during EDL
evolution. The magnitude and temporal
evolution of these corrections are characterized across parametric regimes, revealing systematic departures from standard constant-permittivity and constant-viscosity models, with electroosmotic mobility reductions of up to 65% governed by a characteristic dimensionless parameter. The results predict a characteristic frequency-dependent transition in electroosmotic mobility and dipolar solvent corrections in emerging MHz AC electrokinetic flows. The results provide a solvent-consistent continuum framework for transient nanoscale electroosmotic flows and quantify the impact of molecular solvent structure on electrohydrodynamic transport relevant to modern nanofluidic applications.
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Statistical Mechanics · Cross-listed from quant-ph
Quantum timekeeping and the dynamics of scrambling in critical systems
Devjyoti Tripathy, Federico Centrone and Sebastian Deffner
In this work, we develop a
quantum metrological framework for
quantum chaos by showing that local subsystems of information scrambling systems naturally function as
quantum stopwatches. The reduced
quantum state of a subsystem encodes the passage of time through its growing distinguishability from the initial preparation. Treating time as the estimation parameter, we then derive a generalized
quantum Cramer-Rao bound that directly relates the precision of time estimation to the decay of out-of-time ordered correlators (OTOCs) and subsystem
quantum Fisher information (QFI). As a main result, we obtain continuity bounds for
quantum Lyapunov exponent in terms of the subsystem QFI in quantumly chaotic dynamics. Furthermore, using a scaling analysis based on imaginary-time correlators, we show that the subsystem QFI exhibits universal critical amplification near
quantum phase transitions. Our results are demonstrated and verified by a numerical analysis of the dynamics of a chaotic Ising chain.
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Statistical Mechanics · Cross-listed from hep-th
Jones index from Rényi entropies in the Ising conformal field theory
Valentin Benedetti, Isai Davila-Cuba and Erik Tonni
We study the relation between the Jones index and the Rényi
entropies of two disjoint intervals on the line and of the ground state for a generic value of the Rényi index in the two conformal field theory models given by the Ising model and a free Majorana
fermion, where Haag duality is satisfied. The analytic expressions of the crossing asymmetry for all the submodels displaying a violation of the Haag duality that are closed under the fusion rules are obtained. In the limiting regime where the two intervals become adjacent, the leading term of the expansion of the crossing asymmetry provides the Jones global index, for any finite value of the Rényi index.
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Disordered Systems and Neural Networks
A toy model of a protein prototype reveals nontrivial ultrametricity of the energy landscape
A.Kh. Bikulov and A.P. Zubarev
A model for studying the ultrametricity of the energy landscape in a disordered heteropolymer is presented. It is treated as a simplified model of a
protein molecule in which amino acid residues are modeled as point masses. Pairwise interactions include universal repulsion, the Lennard-Jones potential, the Coulomb potential with screening, and the elastic potential for bonds between adjacent residues. An analogy with
spin glass models is used, allowing the application of replica theory methods. Unlike the standard approach to disordered systems, averaging over disorder is not performed. The overlap between replicas is defined as the Pearson correlation coefficient between the vectors of average pairwise energies, which corresponds to a comparison of thermodynamic averages in the spirit of
spin glass theory. The results of a computational experiment conducted using the developed
algorithm on a graphics processing unit (GPU) are presented. The simulations were performed using a 128-residue-long sequence, with 50 independent disorder realizations and 50 replicas for each sequence at a temperature of T = 1.0. It was found that for 90.0% of the sequences, the distance
matrix between replicas contains more than half of the ultrametric triangles, and nontrivial ultrametricity predominates in 97.8% of them, indicating a hierarchical organization of the energy landscape. A repeated computational experiment for selected sequences confirms the reliability of the observations: 95.5% of them again demonstrated ultrametricity, of which 97.7% showed a predominance of the nontrivial type of ultrametricity. The obtained results confirm Frauenfelder's hypothesis of
protein ultrametricity and pave the way for a systematic study of ultrametric properties in more realistic
protein models.
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Soft Condensed Matter
Boundary-Mediated Phases of Self-Propelled Kuramoto Particles
Francesco Arceri, Vittoria Sposini, Enzo Orlandini et al. (+1 more)
Active
agents can transfer energy to their environment through collective motion, generating accumulation patterns near confining obstacles. Here we investigate how the nature of the microscopic drive-self-propulsion or velocity
alignment-selects distinct accumulation patterns, leading to either delocalized or compact clustered states. We first characterize the dynamical regimes emerging from the interplay of these two driving mechanisms under perfectly reflective or smooth boundary conditions. We then introduce boundary friction and observe a drastic change in the accumulation patterns, with new dynamical phases that are absent in the previous case. By connecting emergent macroscopic structures to their underlying microscopic interactions, this work provides a practical route to infer the dominant interaction ruling boundary-mediated collective behavior, with applications ranging from single-
cell migration to bio-inspired robotics.
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All authors Francesco Arceri, Vittoria Sposini, Enzo Orlandini, Fulvio Baldovin
Soft Condensed Matter
Large dilatational hyperelasticity of glasses en route to cavitation failure
Pawandeep Kaur, Noam Ottolenghi, Edan Lerner et al. (+2 more)
Materials deform elasto-plastically and fail under various loading conditions, typically quantified by the stress triaxiality, which is the ratio between the dilatational (hydrostatic) stress and the deviatoric (shear-like) one. We show that the elasto-plastic deformation of glasses approaching failure qualitatively differ for large and small stress triaxiality levels. Specifically, in the former limit, glasses reveal a strong hyperelastic (nonlinear elastic) response with minute plasticity, largely independently of the quenching rate across the glass transition. Yet, glassy disorder gives rise to significant elastic (reversible) nonaffine deformation, accompanied by the formation of micro-cavities. A small fraction of the latter is irreversible, i.e., survives unloading prior to the onset of failure, and may serve as nucleation sites for failure in the form of large-scale cavitation, involving a topological transition accompanied by the formation of an internal free surface, upon which the glass loses a significant fraction of its load-bearing capacity. These results are contrasted with glass behavior in the limit of vanishing stress triaxiality and their universality across different glass formers is demonstrated. Finally, the implications of our findings for understanding glass deformation and failure under realistic stress conditions are discussed.
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All authors Pawandeep Kaur, Noam Ottolenghi, Edan Lerner, David Richard, Eran Bouchbinder
Mesoscale and Nanoscale Physics
Dynamic charge oscillation in a quantum conductor driven by ultrashort voltage pulses
Lucas Mazzella, Seddik Ouacel and Inès Safi
Time-dependent driving with ultrashort voltage pulses brings
quantum conductors into the non-adiabatic transport regime, where novel dynamical effects emerge. An example of this physics occurs in interferometric systems, where the transmitted charge oscillates as a function of the charge injected by an ultrashort voltage pulse. This behavior has been predicted in a variety of setups, including Fabry-Pérot and Mach-Zehnder interferometers, and more recently in
quantum dots. It is commonly interpreted as resulting from interference between different propagating paths taken by the injected excitation. In this letter, we fully generalize the derivation of such dynamic charge oscillations beyond interferometric devices for a generic
quantum conductor with the single assumption that its DC current is sublinear at large bias. Strikingly, they also extend perturbatively to strongly correlated conductors, showing in particular their robustness against arbitrarily strong Coulomb interactions. To illustrate the generality of our approach, we analyze in detail the case of a
quantum point contact in the fractional
quantum Hall regime, which fulfills the sublinearity condition. We demonstrate that this non-interferometric system exhibit dynamic charge oscillation. Finally, we propose a complementary interpretation of this phenomenon, rooted in the photo-assisted probabilities associated with the voltage pulse.
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Soft Condensed Matter
Electrohydrodynamic Stresses from Hydrogen-Bond Network Dynamics in Water
Pramodt Srinivasula
The resistance of hydrogen-bond networks to ambient flow in water produces viscoelectric stresses and contributes to electrostrictive pressure. Within Onsager's nonequilibrium thermodynamic framework, a
lattice-gas description of aqueous electrolytes is combined with a coarse-grained hydrodynamic representation of hydrogen-bonded molecular networks, where viscous dissipation is modeled through energetically equivalent Brownian entities. This formulation connects molecular structural information from experiments and molecular dynamics to a unified dipolar Poisson-Nernst-Planck-Stokes (dPNP-S) continuum theory, quantitatively reproducing the measured viscoelectric coefficient of Jin et al. (PNAS 2022) and contributions to electrostrictive pressure. These results identify a microscopic mechanism by which hydrogen-bond dynamics influence electrohydrodynamic flow.
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Strongly Correlated Electrons
Orbital dimerization-induced first-order structural phase transition: a case study in La$_3$Ni$_2$O$_7$
Xingchen Shen and Wei Ku
First-order structural phase transition is a common phenomenon in materials that qualitatively alters their physical properties. Yet, the abrupt first-order nature is usually unexplained by realistic computations, implying an omission of important physics in describing the electronic structure of the nearby stable phases. Using the recently discovered nickelate
superconductors La$_3$Ni$_2$O$_7$ as a prototypical example, we demonstrate that such first-order nature is typically beyond intra-atomic correlation considered in state-of-the-art material computations. Instead, a full many-body treatment of low-energy active orbitals reveals a generic inter-atomic "orbital dimerization" mechanism of first-order structural phase transition, corresponding to abrupt energy reduction upon a
spin-singlet bond formation. Such an inter-atomic correlation qualitatively changes not only the essential
lattice bonding but also the characteristics of low-energy electronic properties across the transition. This strong mechanism and the developed computational framework are generally applicable to a wide variety of ionic materials, to produce valuable insights into atomic and electronic structures essential for their physical properties and functionalities.
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Strongly Correlated Electrons
Heat Capacity-A Powerful Tool for Studying Exotic States of Matter
K. Ramesh Kumar, Xudong Huai, Michał J. Winiarski et al. (+2 more)
Heat capacity measurements are a powerful tool that researchers rely on when studying the relationship between microscopic degrees of freedom and macroscopic behavior in condensed matter. This uniqueness stems from heat capacity capturing contributions from
lattice, electronic, and
magnetic components, as well as energy-level populations, enabling an effective approach to studying phase transitions and excitations across different classes of materials. However, analyzing heat capacity data presents a common, appreciable challenge for new researchers. Although comprehensive theoretical aspects of heat capacity are presented in several elegant textbooks, practical application remains a daunting task. To overcome this challenge, this tutorial guides researchers in collecting, analyzing, and interpreting heat capacity data in contemporary
quantum materials. We outline the connections between thermodynamics, heat capacity, and
entropy, as well as measurement methodology and data analysis for representative examples, including
phonon dynamics,
spin waves,
superconductors,
magnetic skyrmions, proximate
quantum spin liquids, and heavy-
fermion materials. Our goal is to provide a concise, accessible guide that enables new researchers to utilize heat capacity as a quantitative lens for understanding exotic states of matter.
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All authors K. Ramesh Kumar, Xudong Huai, Michał J. Winiarski, Allen O. Scheie, Thao T. Tran