In this paper, we investigate the dynamics of a non-Hermitian Su-Schrieffer-Heeger model that arises out of the no-click limit of a monitored SSH model in the Krylov space. We find that the saturation timescale of the complexity associated with the spread of the state in the Krylov subspace increases with the measurement rate, and late time behaviour differs across the PT symmetry transition point. Furthermore, extending the notion of this complexity for subsystems in Krylov space, we find that the scaling of its late time value with subsystem size shows a discontinuous jump across the PT transition point, indicating that it can be used as a suitable order parameter for such transition but not for the measurement-induced transition. Finally, we show that a generalized measure in the Krylov subspace, which contains information about the correlation landscape, such as Quantum Fisher information, which also possesses some structural similarity with the complexity functional, can be a promising probe of the measurement-induced phase.

India

Nilachal Chakrabarti

Neha Nirbhan

Arpan Bhattacharyya

Dynamics of monitored SSH model in Krylov space: from complexity to quantum Fisher information

We revisit the problem of the thermalization process for an Unruh-DeWitt (UDW) detector in de Sitter space. We derive the complete dynamics of the detector in the context of an open quantum system, without utilizing Markovian or RWA approximations. We employ quantum Fisher information (QFI) to estimate the Hubble parameter, which serves as a process function to distinguish the thermalization paths in the detector’s Hilbert space, determined by its local properties, including the detector’s energy gap and its initial state preparation, or by the global spacetime geometry. We find that the non-Markovian contribution generally reduces the QFI compared to the Markovian approximated solution. Regarding arbitrary initial states, the late-time QFI converges to an asymptotic value. In particular, we are interested in the background field within the one-parameter family of α-vacua in de Sitter space. We show that for general choices of $\textit{α}$-vacuum, the asymptotic values of the converged QFI are significantly suppressed compared to previously known results for the Bunch-Davies vacuum.

China

Langxuan Chen

Jun Feng

Quantum Fisher information of a cosmic qubit undergoing non-Markovian de Sitter evolution

We propose novel inflationary primordial gravitational wave (GW) spectral shapes at interferometer-based current and future GW missions to test dark matter (DM) production via gravity-portal. We consider three right-handed neutrinos (RHNs), required to generate Standard Model (SM) neutrino masses via seesaw mechanism, are produced via gravity-portal in early universe. The lightest among them is stable and is the DM candidate of the Universe. The other two RHNs decay and generate matter-antimatter asymmetry due to baryogenesis via leptogenesis. We find that future GW detectors BBO, DECIGO, ET, for instance, are able to probe DM mass for 5 × 106 GeV &lt; M DM &lt; 1.6 × 107 GeV with a signal-to-noise ratio (SNR) &gt; 10, along with the observed amount of baryon asymmetry due to gravitational leptogenesis for heavy RHN mass   <math> <msub> <mi>M</mi> <mi>N</mi> </msub> </math>  $$ {M}_{\mathcal{N}} $$  to be around 8 × 1012 GeV. Employing Fisher matrix forecast analysis, we identify the parameter space involving non-minimal coupling to gravity ξ, reheating temperature of the Universe T rh and DM mass M DM where the GW detector-sensitivities will be the maximum with the least error, along with SNR &gt; 10. Finally, utilizing mock data for each GW detector, we perform MCMC analysis to find out the combined constraints on the various microphysics parameters. We also explore production of other cosmological relics such as QCD axion relic as DM candidate, produced via gravity-portal in early universe. We find that ET, for instance, can probe the decay constant of such DM candidates (fa) as 109 GeV ≲ fa ≲ 1014 GeV for misalignment angle θ  i  ∈ [0.1, π/  <math> <msqrt> <mn>3</mn> </msqrt> </math>  $$ \sqrt{3} $$ ] and ξ = 1 with SNR &gt; 10, whereas this range decreases with the increase of non-minimal coupling. Thus the upcoming GW missions will be able to test such non-thermal DM and baryogenesis scenarios involving very high energy scales, which is otherwise impossible to reach in particle physics experiments in laboratories.

Poland

Anish Ghoshal

Debarun Paul

Supratik Pal

Primordial gravitational waves as probe of dark matter in interferometer missions: Fisher forecast and MCMC

High-energy scattering in pQCD in the Regge limit is described by the evolution of Wilson lines governed by the BK equation [1, 2]. In the leading order, the BK equation is conformally invariant and the eigenfunctions of the linearized BFKL equation are powers. It is a common belief that at d ≠ 4 the BFKL equation is useless since unlike d = 4 case it cannot be solved by usual methods. However, we demonstrate that at critical Wilson-Fisher point of QCD the relevant part of NLO BK restores the conformal invariance so the solutions are again powers. As a check of our approach to high-energy amplitudes at the Wilson-Fisher point, we calculate the anomalous dimensions of twist-2 light-ray operators in the Regge limit j → 1.

United States

I. Balitsky

Italy

G. Chirilli

Conformal BK equation at QCD Wilson-Fisher point

Previous studies have shown that the decoherence of environments generally negatively influences the quantum correlations in the Schwarzschild black hole. In our paper, we find that the decoherence of the generalized amplitude damping (GAD) channel has both positive and negative effects on the quantum coherence of Dirac fields, which means that the decoherence of environments can not only reduce the quantum coherence but also increase the quantum coherence in Schwarzschild spacetime. This result banishes the widespread belief that the decoherence of the environment can only destroy the quantum coherence in curved spacetime. Furthermore, another novel phenomenon has been observed for the first time: with increasing Hawking temperature T, the QFI of physically inaccessible modes rapidly decays from infinity to 0, which may provide a way to detect whether the particles enter the physically inaccessible region or not. This result may provide a new perspective for exploring and analyzing black holes.

Chun-yao Liu

Zheng-wen Long

Qi-liang He

Quantum coherence and quantum Fisher information of Dirac particles in curved spacetime under decoherence

We present a numerical calculation of the Lee-Yang and Fisher zeros of the 2D Ising model using multipoint Padé approximants. We perform simulations for the 2D Ising model with ferromagnetic couplings both in the absence and in the presence of a magnetic field using a cluster spin-flip algorithm. We show that it is possible to extract genuine signature of Lee-Yang and Fisher zeros of the theory through the poles of magnetization and specific heat, using the multipoint Padé method. We extract the poles of magnetization using Padé approximants and compare their scaling with known results. We verify the circle theorem associated to the well known behavior of Lee-Yang zeros. We present our finite volume scaling analysis of the zeros done at <math><mi>T</mi><mo>=</mo><msub><mi>T</mi><mi>c</mi></msub></math> for a few lattice sizes, extracting to a good precision the (combination of) critical exponents <math><mi>β</mi><mi>δ</mi></math>. The computation at the critical temperature is performed after the latter has been determined via the study of Fisher zeros, thus extracting both <math><msub><mi>β</mi><mi>c</mi></msub></math> and the critical exponent <math><mi>ν</mi></math>. Results already exist for extracting the critical exponents for the Ising model in two and three dimensions making use of Fisher and Lee-Yang zeros. In this work, multipoint Padé is shown to be competitive with this respect and thus a powerful tool to study phase transitions.

Germany

Simran Singh

Massimo Cipressi

Francesco Di Renzo

Exploring Lee-Yang and Fisher zeros in the 2D Ising model through multipoint Padé approximants

Relativistic quantum metrology is the study of optimal measurement procedures within systems that have both quantum and relativistic components. Here we use Unruh-DeWitt detectors coupled to a massless scalar field as probes of thermal parameters in different spacetimes via a relativistic quantum metrology analysis. We consider both (2 + 1)-dimensional anti-de Sitter and BTZ black hole spacetimes. We compute the Fisher information to identify characteristics of the black hole spacetime and to compare it to a uniformly accelerating detector in anti-de Sitter space. We find the dependence of the Fisher information on temperature, detector energy gap, black hole mass, interaction time, and the initial state of the detector. We identify strategies that maximize the Fisher information and therefore the precision of estimation.

Canada

Everett Patterson

Robert Mann

Fisher information of a black hole spacetime

A long-standing debate on Unruh effect is about its obscure thermal nature. In this Letter, we use quantum Fisher information (QFI) as an effective probe to explore the thermal nature of Unruh effect from both local and global perspectives. By resolving the full dynamics of UDW detector, we find that the QFI is a time-evolving function of detector's energy gap, Unruh temperature <math><msub><mrow><mi>T</mi></mrow><mrow><mi>U</mi></mrow></msub></math> and particularities of background field, e.g., mass and spacetime dimensionality. We show that the asymptotic QFI whence detector arrives its equilibrium is solely determined by <math><msub><mrow><mi>T</mi></mrow><mrow><mi>U</mi></mrow></msub></math>, demonstrating the global side of Unruh thermality alluded by the KMS condition. We also show that the local side of Unruh effect, i.e., the different ways for the detector to approach the same thermal equilibrium, is encoded in the corresponding time-evolution of the QFI. In particular, we find that with massless scalar background the QFI has unique monotonicity in <math><mi>n</mi><mo>=</mo><mn>3</mn></math> dimensional spacetime, and becomes non-monotonous for <math><mi>n</mi><mo>≠</mo><mn>3</mn></math> models where a local peak value exists at early time and for finite acceleration, indicating an enhanced precision of estimation on Unruh temperature at a relative low acceleration can be achieved. Once the field acquiring mass, the related QFI becomes significantly robust against the Unruh decoherence in the sense that its local peak sustains for a very long time. While coupling to a more massive background, the persistence can even be strengthened and the QFI possesses a larger maximal value. Such robustness of QFI can surely facilitate any practical quantum estimation task.

Jing-Jun Zhang

Quantum Fisher information as a probe for Unruh thermality

In this work we focus on computing the conformal dimensions <math><mi>D</mi><mo>(</mo><msub><mi>j</mi><mi>L</mi></msub><mo>,</mo><msub><mi>j</mi><mi>R</mi></msub><mo>)</mo></math> of local fields that transform in an irreducible representation of <math><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><mo>)</mo><mo>×</mo><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><mo>)</mo></math> labeled with <math><mo>(</mo><msub><mi>j</mi><mi>L</mi></msub><mo>,</mo><msub><mi>j</mi><mi>R</mi></msub><mo>)</mo></math> at the <math><mi>O</mi><mo>(</mo><mn>4</mn><mo>)</mo></math> Wilson-Fisher fixed point using the Monte Carlo method. In the large charge expansion, among the sectors with a fixed large value of <math><mi>j</mi><mo>=</mo><mi>max</mi><mo>(</mo><msub><mi>j</mi><mi>L</mi></msub><mo>,</mo><msub><mi>j</mi><mi>R</mi></msub><mo>)</mo></math>, the leading sector has <math><mo>|</mo><msub><mi>j</mi><mi>L</mi></msub><mo>−</mo><msub><mi>j</mi><mi>R</mi></msub><mo>|</mo><mo>=</mo><mn>0</mn></math> and the subleading one has <math><mo>|</mo><msub><mi>j</mi><mi>L</mi></msub><mo>−</mo><msub><mi>j</mi><mi>R</mi></msub><mo>|</mo><mo>=</mo><mn>1</mn></math>. Since Monte Carlo calculations at large <math><mi>j</mi></math> become challenging in the traditional lattice formulation of the <math><mi>O</mi><mo>(</mo><mn>4</mn><mo>)</mo></math> model, a qubit regularized <math><mi>O</mi><mo>(</mo><mn>4</mn><mo>)</mo></math> lattice model was used recently to compute <math><mi>D</mi><mo>(</mo><mi>j</mi><mo>,</mo><mi>j</mi><mo>)</mo></math>. Here we extend those calculations to the subleading sector. Our Monte Carlo results in the range <math><mn>2</mn><mo>≤</mo><mi>j</mi><mo>≤</mo><mn>20</mn></math> fit well to the expected large <math><mi>j</mi></math> expansion <math><mrow><mi>D</mi><mo>(</mo><mi>j</mi><mo>,</mo><mi>j</mi><mo>−</mo><mn>1</mn><mo>)</mo><mo>−</mo><mi>D</mi><mo>(</mo><mi>j</mi><mo>,</mo><mi>j</mi><mo>)</mo><mo>∼</mo><msub><mrow><mi>λ</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>+</mo><msub><mrow><mi>λ</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>/</mo><msqrt><mrow><mi>j</mi></mrow></msqrt><mo>+</mo><msub><mrow><mi>λ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>/</mo><mi>j</mi><mo>+</mo><msub><mrow><mi>λ</mi></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>/</mo><msup><mrow><mi>j</mi></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></math>, but we have to assume that at least one of the purely quantum mechanical contributions <math><msub><mi>λ</mi><mn>0</mn></msub></math> or <math><msub><mi>λ</mi><mn>1</mn></msub></math> is nonzero. Assuming <math><msub><mi>λ</mi><mn>0</mn></msub><mo>=</mo><mn>0</mn></math> as conjectured recently, we find <math><msub><mi>λ</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>≈</mo><mn>2.1</mn><mo>(</mo><mn>1</mn><mo>)</mo></math>, <math><msub><mi>λ</mi><mn>1</mn></msub><mo>≈</mo><mn>2.3</mn><mo>(</mo><mn>2</mn><mo>)</mo></math>, and <math><msub><mi>λ</mi><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>≈</mo><mn>1.2</mn><mo>(</mo><mn>2</mn><mo>)</mo></math>.

Debasish Banerjee

Shailesh Chandrasekharan

Subleading conformal dimensions at the O(4) Wilson-Fisher fixed point

Using the corner-transfer matrix renormalization group approach, we revisit the three-state chiral Potts model on the square lattice, a model proposed in the eighties to describe commensurate-incommensurate transitions at surfaces, and with direct relevance to recent experiments on chains of Rydberg atoms. This model was suggested by Huse and Fisher to have a chiral transition in the vicinity of the Potts point, a possibility that turned out to be very difficult to definitely establish or refute numerically. Our results confirm that the transition changes character at a Lifshitz point that separates a line of Pokrosky-Talapov transitions far enough from the Potts point from a line of direct continuous order-disorder transition close to it. Thanks to the accuracy of the numerical results, we have been able to base the analysis entirely on effective exponents to deal with the crossovers that have hampered previous numerical investigations. The emerging picture is that of a new universality class with exponents that do not change between the Potts point and the Lifshitz point, and that appear to be consistent with those of a self-dual version of the model, namely correlation lengths exponents <math><msub><mrow><mi>ν</mi></mrow><mrow><mi>x</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>/</mo><mn>3</mn></math> in the direction of the asymmetry and <math><msub><mrow><mi>ν</mi></mrow><mrow><mi>y</mi></mrow></msub><mo>=</mo><mn>1</mn></math> perpendicular to it, an incommensurability exponent <math><mover><mrow><mi>β</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>=</mo><mn>2</mn><mo>/</mo><mn>3</mn></math>, a specific heat exponent that keeps the value <math><mi>α</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>3</mn></math> of the three-state Potts model, and a dynamical exponent <math><mi>z</mi><mo>=</mo><mn>3</mn><mo>/</mo><mn>2</mn></math>. These results are in excellent agreement with experimental results obtained on reconstructed surfaces in the nineties, and shed light on recent Kibble-Zurek experiments on the period-3 phase of chains of Rydberg atoms.

Switzerland

Samuel Nyckees

Jeanne Colbois

Frédéric Mila

Identifying the Huse-Fisher universality class of the three-state chiral Potts model