Observation of many-body Fock space dynamics in two dimensions

Quantum many-body simulation provides a straightforward way to understand fundamental physics and connect with quantum information applications. However, suffering from exponentially growing Hilbert space size, characterization in terms of few-body probes in real space is often insufficient to tackle challenging problems such as quantum critical behavior and many-body localization (MBL) in higher dimensions. Here, we experimentally employ a new paradigm on a superconducting quantum processor, exploring such elusive questions from a Fock space view: mapping the many-body system onto an unconventional Anderson model on a complex Fock space network of many-body states. By observing the wave packet propagating in Fock space and the emergence of a statistical ergodic ensemble, we reveal a fresh picture for characterizing representative many-body dynamics: thermalization, localization, and scarring. In addition, we observe a quantum critical regime of anomalously enhanced wave packet width and deduce a critical point from the maximum wave packet fluctuations, which lend support for the two-dimensional MBL transition in finite-sized systems. Our work unveils a new perspective of exploring many-body physics in Fock space, demonstrating its practical applications on contentious MBL aspects such as criticality and dimensionality. Moreover, the entire protocol is universal and scalable, paving the way to finally solve a broader range of controversial many-body problems on future larger quantum devices.Comment: 8 pages, 4 figures + supplementary informatio

Review on the Modeling of Electrostatic MEMS

Electrostatic-driven microelectromechanical systems devices, in most cases, consist of couplings of such energy domains as electromechanics, optical electricity, thermoelectricity, and electromagnetism. Their nonlinear working state makes their analysis complex and complicated. This article introduces the physical model of pull-in voltage, dynamic characteristic analysis, air damping effect, reliability, numerical modeling method, and application of electrostatic-driven MEMS devices

Improved measurements of the Dalitz decays η/η′→γe+e−\eta/\eta'\rightarrow\gamma e^{+}e^{-}

Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector, improved measurements of the Dalitz decays $\eta/\eta'\rightarrow\gamma e^+e^-$ are performed, where the $\eta$ and $\eta'$ are produced through the radiative decays $J/\psi\rightarrow\gamma \eta/\eta'$. The branching fractions of $\eta\rightarrow\gamma e^+e^-$ and $\eta'\rightarrow\gamma e^+e^-$ are measured to be $(7.07 \pm 0.05 \pm 0.23)\times10^{-3}$ and $(4.83\pm0.07\pm0.14)\times10^{-4}$, respectively. Within the single pole model, the parameter of electromagnetic transition form factor for $\eta\rightarrow\gamma e^+e^-$ is determined to be $\Lambda_{\eta}=(0.749 \pm 0.027 \pm 0.007)~ {\rm GeV}/c^{2}$. Within the multi-pole model, we extract the electromagnetic transition form factors for $\eta'\rightarrow\gamma e^+e^-$ to be $\Lambda_{\eta'} = (0.802 \pm 0.007\pm 0.008)~ {\rm GeV}/c^{2}$ and $\gamma_{\eta'} = (0.113\pm0.010\pm0.002)~ {\rm GeV}/c^{2}$. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the $\eta$ and $\eta'$ are calculated to be $(0.645 \pm 0.023 \pm 0.007 )~ {\rm fm}$ and $(0.596 \pm 0.005 \pm 0.006)~ {\rm fm}$, respectively. In addition, we search for the dark photon in $\eta/\eta^\prime\rightarrow\gamma e^{+}e^{-}$, and the upper limits of the branching fractions as a function of the dark photon are given at 90\% confidence level

Measurements of Born Cross Sections for e+e−→Λc+Λˉc(2595)−+c.c.e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2595)^- + {\rm c.c.} and e+e−→Λc+Λˉc(2625)−+c.c.e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2625)^- + {\rm c.c.} at s=\sqrt{s}=4918.0 and 4950.9 MeV

Using $e^+e^-$ collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2595)^- + \rm{c.c.}$ and $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2625)^- + \rm{c.c.}$ are measured for the first time at center-of-mass energies of $\sqrt{s}=4918.0$ and 4950.9 MeV. Non-zero cross sections are observed very close to the production threshold. The measured Born cross sections of $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2625)^- + \rm{c.c.}$ are about $2\sim3$ times greater than those of $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2595)^- + \rm{c.c.}$, thereby indicating that the exotic structure potentially exists in the excited charmed baryons. The Born cross sections are $15.6\pm3.1\pm0.9$ pb and $29.4\pm3.7\pm2.7$ pb for $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2595)^- + \rm{c.c.}$, and are $43.4\pm4.0\pm4.1$ pb and $76.8\pm6.5\pm4.2$ pb for $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2625)^- +\rm{c.c.}$ at $\sqrt s=4918.0$ and 4950.9 MeV, respectively. Based on the polar angle distributions of the $\bar{\Lambda}_{c}(2625)^-$ and $\Lambda_{c}(2625)^+$, the form-factor ratios $\sqrt{|G_{E}|^2 + 3|G_{M}|^2}/|G_{C}|$ are determined for $e^+e^-\to \Lambda_{c}^+ \bar{\Lambda}_{c}(2625)^- + \rm{c.c.}$ for the first time, which are $5.95\pm4.07\pm0.15$ and $0.94\pm0.32\pm0.02$ at $\sqrt s=4918.0$ and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic.Comment: 10 pages, 6 figure