arXiv subjects

Henry L. Nourse

Publications and source records attributed to Henry L. Nourse.

6 recordsLinked to original sources

arXiv2026

Programmable quantum simulation of anharmonic dynamics

Continuous-variable-discrete-variable (CV-DV) quantum simulators offer a natural route to simulating bosonic dynamics relevant to many branches of physics and chemistry. However, programmable simulation of arbitrary dynamics is an outstanding challenge. In particular, simulating anharmonic dynamics, which is ubiquitous across the physical sciences, is challenging due to the highly harmonic nature of oscillators used in CV-DV simulators. Here, we experimentally demonstrate programmable CV-DV quantum simulation of anharmonic dynamics in a range of double-well potentials, implemented in a trapped-ion system. We synthesise the time-evolution operators using a bosonic-quantum-signal-processing subroutine, which allows the potential to be tuned between experiments by controlling classical experimental parameters. We observe coherent dynamics in various double-well potentials, where a wavepacket tunnels through the potential barrier, and we suppress this effect by programmatically introducing asymmetry.

quant-ph↗

arXiv2026

Accelerating dynamical mean-field theory convergence by preconditioning with computationally cheaper quantum embedding methods

Dynamical mean-field theory (DMFT) is a cornerstone technique for studying strongly correlated electronic systems. However, each DMFT step is computationally demanding, and many iterations can be required to achieve convergence. Here, we accelerate the convergence of DMFT by initializing its self-consistent cycle with solutions from computationally cheaper and more approximate methods. We compare the initialization with the non-interacting solution to a range of quantum embedding compatible approaches: Hartree-Fock, the Hubbard-I approximation, rotationally invariant slave bosons (RISB), and its ghost extension (g-RISB). We find that these initializations can reduce the number of DMFT iterations by up to an order of magnitude, with g-RISB providing the most effective and reliable benefits. In most regimes, initializing with g-RISB and performing a single DMFT iteration suffices to recover the full dynamical structure. The improvement in convergence is controlled by the initial solution's accuracy in the low-energy part of the self-energy, on the scale of the non-interacting bandwidth. This strategy is especially effective at the Mott insulator-metal transition, where an initialization from the non-interacting limit can lead to a breakdown of DMFT due to the sign problem. Our results establish the usage of accurate yet cheaper quantum embedding methods as a powerful means to substantially reduce the computational cost of DMFT, particularly in regimes where convergence is slow or prone to failure.

cond-mat.str-el↗

arXiv2025

Using bosons to improve resource efficiency of quantum simulation of vibronic molecular dynamics

Simulating chemical dynamics is computationally challenging, especially for nonadiabatic dynamics, where numerically exact classical simulations scale exponentially with system size, becoming intractable for even small molecules. On quantum computers, chemical dynamics can be simulated efficiently using either universal, qubit-only devices or specialized mixed-qudit-boson (MQB) simulators, which natively host electronic and vibrational degrees of freedom. Here, we compare the quantum resources required for a qubit-only approach to achieve the same accuracy as an MQB device at simulating nonadiabatic molecular dynamics. We find that MQB simulations require orders-of-magnitude fewer quantum operations than qubit-only simulations, with a one-gate MQB circuit requiring a qubit-equivalent circuit volume of over 400,000 when simulating an isolated molecule, which increases to over ten million when environmental effects are included. These estimates assume perfect qubits and gates, and would increase by additional orders of magnitude if error correction were used for fault tolerance. When errors are small, the advantage of MQB simulators becomes even larger as system size increases. Our results highlight the enormous resource advantages of representing non-qubit chemical degrees of freedom natively, rather than encoding them into qubits.

quant-ph↗

arXiv2025

Fingerprints of collective magnetic excitations in inelastic electron tunneling spectroscopy

Spin-flip inelastic electron tunneling spectroscopy allows magnetic materials to be probed at the single-atom level via scanning tunneling microscopy. Previously, the local spectral weight of spin excitations of small systems has been deduced from discrete steps in the differential conductance. However, this is not viable for large systems. We show that the local spin density of states can be measured via the double differential conductance. This contrasts with elastic measurements where the local density of electronic states is deduced from the differential conductance. We study the tunneling currents of the spin-1/2 and -1 Heisenberg chains and propose a method to probe zero-frequency modes.

cond-mat.str-el↗

arXiv2024

Competing quantum effects in spin crossover chains: spin-orbit coupling, magnetic exchange, and elastic interactions

We derive and study a model of square planar, d8 spin crossover materials that treats elastic, magnetic and spin-orbit interactions on an equal footing. For 1D chains density matrix renormalization group calculations show that the competition between these interactions leads to six different phases. For weak spin-orbit coupling (SOC) and large antiferromagnetic interactions we find a symmetry protected topological (SPT) Haldane phase. This is equivalent to the Haldane-large-D phase transition driven by single ion anisotropy(D) in the spin-one Heisenberg model. For strong SOC the Sz=+-1 HS states are high-energy excitations. Thus, the system can be understood as a transverse field Ising model with the SOC playing the role of the transverse field. Consistent with this, we find a quantum phase transition between the THS phase and a quantum disordered (QD) phase. However, if the magnetic coupling is non-zero or the HS and LS states of a single molecule are non-degenerate the Z2 (Ising) symmetry is broken and the phase transition becomes a crossover. Thus, the QD phase and the THS phases are adiabatically connected, as, equivalently, are the large-D phase of the spin-one Heisenberg model and the quantum disordered phase of the transverse field Ising model. We also find a ferroelastic LS phase, and antierroelastic phase, with alternating HS and LS complexes, and a dimer phase, which results from the competition between antiferromagnetic and antiferroelastic interactions.

cond-mat.str-el↗

arXiv2024

Local gate control of Mott metal-insulator transition in a 2D metal-organic framework

Electron-electron interactions in materials lead to exotic many-body quantum phenomena including Mott metal-insulator transitions (MITs), magnetism, quantum spin liquids, and superconductivity. These phases depend on electronic band occupation and can be controlled via the chemical potential. Flat bands in two-dimensional (2D) and layered materials with a kagome lattice enhance electronic correlations. Although theoretically predicted, correlated-electron Mott insulating phases in monolayer 2D metal-organic frameworks (MOFs) with a kagome structure have not yet been realised experimentally. Here, we synthesise a 2D kagome MOF on a 2D insulator. Scanning tunnelling microscopy (STM) and spectroscopy reveal a MOF electronic energy gap of ~200 meV, consistent with dynamical mean field theory predictions of a Mott insulator. Combining template-induced (via work function variations of the substrate) and STM probe-induced gating, we locally tune the electron population of the MOF kagome bands and induce Mott MITs. These findings enable technologies based on electrostatic control of many-body quantum phases in 2D MOFs.

cond-mat.str-el↗