arXiv subjects

S. Ansari

Publications and source records attributed to S. Ansari.

7 recordsLinked to original sources

arXiv2026

Reply to Comment on "Scaling and universality at noisy quench dynamical quantum phase transitions"

The Comment by J. Sirker [arXiv:2511.16509] raises an important issue concerning dynamical quantum phase transitions (DQPTs) in noisy and mixed-state dynamics, namely that the extension of the Loschmidt echo from pure to mixed states is not unique and different extensions preserve different physical properties. The Comment examines a noise-averaged mixed-state fidelity and shows that DQPTs cannot occur for any nonzero noise when the return rate is defined through the Uhlmann-Bures fidelity of the noise-averaged density matrix. This conclusion is valid for the mixed-state fidelity observable discussed in the Comment and is consistent with prior studies [https://doi.org/10.1103/PhysRevB.109.L180303, arXiv:2504.03005]. Our article [https://doi.org/10.1103/mkll-nd46] investigated a different operationally defined quantity: the logarithm of the Loschmidt echo obtained by first determining the noise-averaged excitation probabilities generated during the noisy ramp and then performing a coherent post-ramp evolution of a pure state constructed from these noise-averaged transition probabilities. As emphasized explicitly in our original publication, this observable is defined through an operational assumption and is not the same quantity as the mixed-state fidelity. The nonanalyticities reported in Ref. [https://doi.org/10.1103/mkll-nd46] therefore concern this two-stage operational protocol and should not be identified with zeros of the Uhlmann-Bures fidelity. There is therefore no direct contradiction between the theorem established for the Uhlmann-Bures return rate and the conclusions obtained for the different operational protocol studied in Ref. [https://doi.org/10.1103/mkll-nd46].

cond-mat.stat-mech↗

arXiv2026

A research roadmap for assessing the feasibility of warming Mars

This roadmap outlines research pathways to determine whether Mars could be warmed with non-biological methods. It does not presuppose that warming Mars is desirable; its purpose is to identify what would need to be true for Mars to be warmed, what it would cost, and what could go wrong. Three complementary research tracks appear promising. Solid-state greenhouse membranes offer local warming, aiding water harvesting, food production, and oxygen supply near human bases. Orbiting reflectors can warm key sites such as bases and CO$_2$-ice reservoirs, although a large combined area would be required. Strengthening Mars' natural greenhouse effect might warm large regions or the globe, although many aspects remain to be worked out. Each approach carries scientific and technical risks that research must address. Near-term priorities are on-Earth testing of key parameters that will determine whether engineered aerosol warming is realistically possible, assessing whether exponential production of bioplastic habitats is possible, and designing at-Mars process experiments. In the near term, the research proposed here is closely aligned with and supports research needed to understand Mars' atmosphere and volatile evolution and hazards to human explorers. The main external uncertainty is whether or not launch costs continue to fall. This is early-stage research, and we discuss key near-term decision points, alternative pathways, and payoffs if research outcomes are negative. We also outline build-out pathways if research succeeds and demand exists. Relatively modest research investments would keep open the option of extending life beyond Earth as Mars' scientific exploration continues.

astro-ph.IM↗

arXiv2024

Shape evolution in even-mass $^{98-104}$Zr isotopes via lifetime measurements using the $\gamma\gamma$-coincidence technique

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first $2^+$ state and the increase in the transition strength B(E2; $2_1^\rightarrow 0_1^+$ going from $^{98}$Zr to $^{100}$Zr has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the $\gamma\gamma$-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in $^{98-104}$Zr carried out to extract reduced transition probabilities. The new lifetime values in $\gamma\gamma$-coincidence and $\gamma$-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock-Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

nucl-ex↗

arXiv2022

Improved measurement of the $0_2^+\rightarrow0_1^+$ E0 transition strength for $^{72}$Se using the SPICE spectrometer

The selenium isotopes lie at the heart of a tumultuous region of the nuclear chart where shape coexistence effects grapple with neutron-proton pairing correlations, triaxiality, and the impending proton dripline. In this work a study of $^{72}$Se by internal conversion electron and $γ$-ray spectroscopy was undertaken with the SPICE and TIGRESS arrays. New measurements of the branching ratio and lifetime of the $0_2^+$ state were performed yielding a determination of $ρ^2(E0;0_2^+{\rightarrow}0_1^+)=29(3)$ milliunits. two state mixing calculations were performed that highlighted the importance of interpretation of such $E0$ strength values in the context of shape-coexistence.

nucl-ex↗

arXiv2014

Observations of $λ/4$ structure in a low-loss radiofrequency-dressed optical lattice

We load a Bose-Einstein condensate into a one-dimensional (1D) optical lattice altered through the use of radiofrequency (rf) dressing. The rf resonantly couples the three levels of the $^{87}$Rb $F=1$ manifold and combines with a spin-dependent "bare" optical lattice to result in adiabatic potentials of variable shape, depth, and spatial frequency content. We choose dressing parameters such that the altered lattice is stable over lifetimes exceeding tens of ms at higher depths than in previous work. We observe significant differences between the BEC momentum distributions of the dressed lattice as compared to the bare lattice, and find general agreement with a 1D band structure calculation informed by the dressing parameters. Previous work using such lattices was limited by very shallow dressed lattices and strong Landau-Zener tunnelling loss between adiabatic potentials, equivalent to failure of the adiabatic criterion. In this work we operate with significantly stronger rf coupling (increasing the avoided-crossing gap between adiabatic potentials), observing dressed lifetimes of interest for optical lattice-based analogue solid-state physics.

cond-mat.quant-gas↗

arXiv2009

Absorption on horizon-wrapped branes

We compute the absorption cross section of space-time scalars on a static D2 rane, in global coordinates, wrapped on the S^2 of an AdS_2 X S^2 X CY_3 geometry. We discuss its relevance for the construction of the dual quantum mechanics of Calabi-Yau black holes.

hep-th↗

arXiv2007

Supersymmetric Branes in Generic M-Theory Attractor Geometries

For a given attractor black hole with generic D6-D4-D2-D0-charges in four dimensions we identify the set of supersymmetric branes, static or stationary in global coordinates, of the corresponding eleven-dimensional near horizon geometry. The set of these BPS states, which includes branes which partially or fully wrap the horizon, should play a role in understanding the partition function of black holes with D6-charges.

hep-th↗