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Transformer neural networks and quantum simulators: a hybrid approach for simulating strongly correlated systems

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-26 DOI: 10.22331/q-2025-03-26-1675

Hannah Lange, Guillaume Bornet, Gabriel Emperauger, Cheng Chen, Thierry Lahaye, Stefan Kienle, Antoine Browaeys, Annabelle Bohrdt

{"title":"Transformer neural networks and quantum simulators: a hybrid approach for simulating strongly correlated systems","authors":"Hannah Lange, Guillaume Bornet, Gabriel Emperauger, Cheng Chen, Thierry Lahaye, Stefan Kienle, Antoine Browaeys, Annabelle Bohrdt","doi":"10.22331/q-2025-03-26-1675","DOIUrl":"https://doi.org/10.22331/q-2025-03-26-1675","url":null,"abstract":"Owing to their great expressivity and versatility, neural networks have gained attention for simulating large two-dimensional quantum many-body systems. However, their expressivity comes with the cost of a challenging optimization due to the in general rugged and complicated loss landscape. Here, we present a hybrid optimization scheme for neural quantum states (NQS), involving a data-driven pretraining with numerical or experimental data and a second, Hamiltonian-driven optimization stage. By using both projective measurements from the computational basis as well as expectation values from other measurement configurations such as spin-spin correlations, our pretraining gives access to the sign structure of the state, yielding improved and faster convergence that is robust w.r.t. experimental imperfections and limited datasets. We apply the hybrid scheme to the ground state search for the 2D transverse field Ising model and dipolar XY model on $6times 6$ and $10times 10$ square lattices with a patched transformer wave function, using numerical data as well as experimental data from a programmable Rydberg quantum simulator [Chen et al., Nature 616 (2023)], and show that the information from a second measurement basis highly improves the performance. Our work paves the way for a reliable and efficient optimization of neural quantum states.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"35 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Entanglement of Disjoint Intervals in Dual-Unitary Circuits: Exact Results

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-26 DOI: 10.22331/q-2025-03-26-1678

Alessandro Foligno, Bruno Bertini

{"title":"Entanglement of Disjoint Intervals in Dual-Unitary Circuits: Exact Results","authors":"Alessandro Foligno, Bruno Bertini","doi":"10.22331/q-2025-03-26-1678","DOIUrl":"https://doi.org/10.22331/q-2025-03-26-1678","url":null,"abstract":"The growth of the entanglement between two disjoint intervals and its complement after a quantum quench is regarded as a dynamical chaos indicator. Namely, it is expected to show qualitatively different behaviours depending on whether the underlying microscopic dynamics is chaotic or integrable. So far, however, this could only be verified in the context of conformal field theories. Here we present an exact confirmation of this expectation in a class of interacting microscopic Floquet systems on the lattice, i.e., dual-unitary circuits. These systems can either have $zero$ or a $textit{super extensive}$ number of conserved charges: the latter case is achieved via fine-tuning. We show that, for $almost$ all dual unitary circuits on qubits and for a large family of dual-unitary circuits on qudits the asymptotic entanglement dynamics agrees with what is expected for chaotic systems. On the other hand, if we require the systems to have conserved charges, we find that the entanglement displays the qualitatively different behaviour expected for integrable systems. Interestingly, despite having many conserved charges, charge-conserving dual-unitary circuits are in general not Yang-Baxter integrable.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"37 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143712828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Mpemba effect and super-accelerated thermalization in the damped quantum harmonic oscillator

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-26 DOI: 10.22331/q-2025-03-26-1677

Stefano Longhi

{"title":"Mpemba effect and super-accelerated thermalization in the damped quantum harmonic oscillator","authors":"Stefano Longhi","doi":"10.22331/q-2025-03-26-1677","DOIUrl":"https://doi.org/10.22331/q-2025-03-26-1677","url":null,"abstract":"The behavior of systems far from equilibrium is often complex and unpredictable, challenging and sometimes overturning the physical intuition derived from equilibrium scenarios. One striking example of this is the Mpemba effect, which implies that non-equilibrium states can sometimes relax more rapidly when they are further from equilibrium. Despite a rich historical background, the precise conditions and mechanisms behind this phenomenon remain unclear. Recently, there has been growing interest in investigating accelerated relaxation and Mpemba-like effects within quantum systems. In this work, we explore a quantum manifestation of the Mpemba effect in a simple and paradigmatic model of open quantum systems: the damped quantum harmonic oscillator, which describes the relaxation of a bosonic mode in contact with a thermal bath at finite temperature $T$. By means of an exact analytical analysis of the relaxation dynamics based on the method of moments in both population and coherence subspaces, we demonstrate that any initial distribution of populations with the first $r$ moments exactly matching those of the equilibrium distribution shows a super-accelerated relaxation to equilibrium at a rate linearly increasing with $r$, leading to a pronounced Mpemba effect. In particular, one can find a broad class of far-from-equilibrium distributions that relax to equilibrium faster than any other initial thermal state with a temperature $T'$ arbitrarily close to $T$. The super-accelerated relaxation effect is shown to persist even for a broad class of initial states with non-vanishing coherences, and a general criterion for the observation of super-accelerated thermalization is presented.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"71 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143702861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Fault-tolerant Quantum Error Correction Using a Linear Array of Emitters

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-26 DOI: 10.22331/q-2025-03-26-1676

Jintae Kim, Jung Hoon Han, Isaac H. Kim

引用次数: 0

Quantum Algorithms for the Pathwise Lasso 路径套索的量子算法

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1674

Joao F. Doriguello, Debbie Lim, Chi Seng Pun, Patrick Rebentrost, Tushar Vaidya

{"title":"Quantum Algorithms for the Pathwise Lasso","authors":"Joao F. Doriguello, Debbie Lim, Chi Seng Pun, Patrick Rebentrost, Tushar Vaidya","doi":"10.22331/q-2025-03-25-1674","DOIUrl":"https://doi.org/10.22331/q-2025-03-25-1674","url":null,"abstract":"We present a novel quantum high-dimensional linear regression algorithm with an $ell_1$-penalty based on the classical LARS (Least Angle Regression) pathwise algorithm. Similarly to available classical algorithms for Lasso, our quantum algorithm provides the full regularisation path as the penalty term varies, but quadratically faster per iteration under specific conditions. A quadratic speedup on the number of features $d$ is possible by using the simple quantum minimum-finding subroutine from Dürr and Hoyer (arXiv'96) in order to obtain the joining time at each iteration. We then improve upon this simple quantum algorithm and obtain a quadratic speedup both in the number of features $d$ and the number of observations $n$ by using the approximate quantum minimum-finding subroutine from Chen and de Wolf (ICALP'23). In order to do so, we approximately compute the joining times to be searched over by the approximate quantum minimum-finding subroutine. As another main contribution, we prove, via an approximate version of the KKT conditions and a duality gap, that the LARS algorithm (and therefore our quantum algorithm) is robust to errors. This means that it still outputs a path that minimises the Lasso cost function up to a small error if the joining times are only approximately computed. Furthermore, we show that, when the observations are sampled from a Gaussian distribution, our quantum algorithm's complexity only depends polylogarithmically on $n$, exponentially better than the classical LARS algorithm, while keeping the quadratic improvement on $d$. Moreover, we propose a dequantised version of our quantum algorithm that also retains the polylogarithmic dependence on $n$, albeit presenting the linear scaling on $d$ from the standard LARS algorithm. Finally, we prove query lower bounds for classical and quantum Lasso algorithms.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"28 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Dipole-dipole interactions mediated by a photonic flat band

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1671

Enrico Di Benedetto, Alejandro Gonzalez-Tudela, Francesco Ciccarello

引用次数: 0

Tensor Product Structure Geometry under Unitary Channels

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1668

Faidon Andreadakis, Paolo Zanardi

{"title":"Tensor Product Structure Geometry under Unitary Channels","authors":"Faidon Andreadakis, Paolo Zanardi","doi":"10.22331/q-2025-03-25-1668","DOIUrl":"https://doi.org/10.22331/q-2025-03-25-1668","url":null,"abstract":"In quantum many-body systems, complex dynamics delocalize the physical degrees of freedom. This spreading of information throughout the system has been extensively studied in relation to quantum thermalization, scrambling, and chaos. Locality is typically defined with respect to a tensor product structure (TPS) which identifies the local subsystems of the quantum system. In this paper, we investigate a simple geometric measure of operator spreading by quantifying the distance of the space of local operators from itself evolved under a unitary channel. We show that this TPS distance is related to the scrambling properties of the dynamics between the local subsystems and coincides with the entangling power of the dynamics in the case of a symmetric bipartition. Additionally, we provide sufficient conditions for the maximization of the TPS distance and show that the class of 2-unitaries provides examples of dynamics that achieve this maximal value. For Hamiltonian evolutions at short times, the characteristic timescale of the TPS distance depends on scrambling rates determined by the strength of interactions between the local subsystems. Beyond this short-time regime, the behavior of the TPS distance is explored through numerical simulations of prototypical models exhibiting distinct ergodic properties, ranging from quantum chaos and integrability to Hilbert space fragmentation and localization.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"57 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143695813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Multi-Armed Bandits and Quantum Channel Oracles

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1672

Simon Buchholz, Jonas M. Kübler, Bernhard Schölkopf

引用次数: 0

Low-overhead non-Clifford fault-tolerant circuits for all non-chiral abelian topological phases

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1673

Andreas Bauer

{"title":"Low-overhead non-Clifford fault-tolerant circuits for all non-chiral abelian topological phases","authors":"Andreas Bauer","doi":"10.22331/q-2025-03-25-1673","DOIUrl":"https://doi.org/10.22331/q-2025-03-25-1673","url":null,"abstract":"We propose a family of explicit geometrically local circuits on a 2-dimensional planar grid of qudits, realizing any abelian non-chiral topological phase as an actively error-corrected fault-tolerant memory. These circuits are constructed from measuring 1-form symmetries in discrete fixed-point path integrals, which we express through cellular cohomology and higher-order cup products. The specific path integral we use is the abelian Dijkgraaf-Witten state sum on a 3-dimensional cellulation, which is a spacetime representation of the twisted quantum double model. The resulting circuits are based on a syndrome extraction circuit of the (qudit) stabilizer toric code, into which we insert non-Clifford phase gates that implement the “twist''. The overhead compared to the toric code is moderate, in contrast to known constructions for twisted abelian phases. We also show that other architectures for the (qudit) toric code phase, like measurement-based topological quantum computation or Floquet codes, can be enriched with phase gates to implement twisted quantum doubles instead of their untwisted versions. As a further result, we prove fault tolerance under arbitrary local (including non-Pauli) noise for a very general class of topological circuits that we call 1-form symmetric fixed-point circuits. This notion unifies the circuits in this paper as well as the stabilizer toric code, subsystem toric code, measurement-based topological quantum computation, or the (CSS) honeycomb Floquet code. We also demonstrate how our method can be adapted to construct fault-tolerant circuits for specific non-Abelian phases. In the appendix we present an explicit combinatorial procedure to define formulas for higher cup products on arbitrary cellulations, which might be interesting in its own right to the TQFT and topological-phases community.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"24 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703269","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Wavefunction branching: when you can’t tell pure states from mixed states

IF 6.4 2区物理与天体物理

Quantum Pub Date : 2025-03-25 DOI: 10.22331/q-2025-03-25-1670

Jordan K. Taylor, Ian P. McCulloch

{"title":"Wavefunction branching: when you can’t tell pure states from mixed states","authors":"Jordan K. Taylor, Ian P. McCulloch","doi":"10.22331/q-2025-03-25-1670","DOIUrl":"https://doi.org/10.22331/q-2025-03-25-1670","url":null,"abstract":"We propose a definition of wavefunction \"branchings\": quantum superpositions which can't be feasibly distinguished from the corresponding mixed state, even under time evolution. Our definition is largely independent of interpretations, requiring only that it takes many more local gates to swap branches than to distinguish them. We give several examples of states admitting such branch decompositions. Under our definition, we argue that attempts to get relative-phase information between branches will fail without frequent active error correction, that branches are effectively the opposite of good error-correcting codes, that branches effectively only grow further apart in time under natural evolution, that branches tend to absorb spatial entanglement, that branching is stronger in the presence of conserved quantities, and that branching implies effective irreversibility. Identifying these branch decompositions in many-body quantum states could shed light on the emergence of classicality, provide a metric for experimental tests at the quantum/ classical boundary, and allow for longer numerical time evolution simulations. We see this work as a generalization of the basic ideas of environmentally-induced decoherence to situations with no clear system/ environment split.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"24 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0