arXiv subjects

Mor M. Roses

Publications and source records attributed to Mor M. Roses.

5 recordsLinked to original sources

arXiv2024

Molecular groundstate determination via short pulses on superconducting qubits

Quantum computing is currently hindered by hardware noise. We present a freestyle superconducting pulse optimization method, incorporating two-qubit channels, which enhances flexibility, execution speed, and noise resilience. A minimal 0.22 ns pulse is shown to determine the H2 groundstate to within chemical accuracy upon real-hardware, approaching the quantum speed limit. Similarly, a pulse significantly shorter than circuit-based counterparts is found for the LiH molecule, attaining state-of-the-art accuracy. The method is general and can potentially accelerate performance across various quantum computing components and hardware.

quant-ph↗

arXiv2023

Dissipative mean-field theory of IBM utility experiment

In spite of remarkable recent advances, quantum computers still lack useful applications. A promising direction for such utility is offered by the simulation of the dynamics of many-body quantum systems, which cannot be efficiently computed classically. Recently, IBM used a superconducting quantum computer to simulate a kicked quantum Ising model with large numbers of qubits and time steps. These results were later reproduced using numerical techniques based on tensor networks and Clifford expansion. In this work, we analyze the experiment in the eyes of a simple-minded mean-field approximation. We treat neighboring qubits as a self-consistent source of dephasing and express them in terms of Kraus operators. Although our approach completely disregards entanglement between qubits, it captures the overall dependence of physical observables as a function of time and external magnetic field. This observation can help rationalize the success of the quantum computer in solving this specific problem.

quant-ph↗

arXiv2021

Simulating long-range hopping with periodically-driven superconducting qubits

Quantum computers are a leading platform for the simulation of many-body physics. This task has been recently facilitated by the possibility to program directly the time-dependent pulses sent to the computer. Here, we use this feature to simulate quantum lattice models with long-range hopping. Our approach is based on an exact mapping between periodically driven quantum systems and one-dimensional lattices in the synthetic Floquet direction. By engineering a periodic drive with a power-law spectrum, we simulate a lattice with long-range hopping, whose decay exponent is freely tunable. We propose and realize experimentally two protocols to probe the long tails of the Floquet eigenfunctions and to identify a scaling transition between weak and strong long-range couplings. Our work offers a useful benchmark of pulse engineering and opens the route towards quantum simulations of rich nonequilibrium effects.

quant-ph↗

arXiv2019

Fermionic formalism for driven-dissipative multi-level systems

We present a fermionic description of non-equilibrium multi-level systems. Our approach uses the Keldysh path integral formalism and allows us to take into account periodic drives, as well as dissipative channels. The technique is based on the Majorana fermion representation of spin-1/2 models which follows earlier applications in the context of spin and Kondo systems. We apply this formalism to problems of increasing complexity: a dissipative two-level system, a driven-dissipative multi-level atom, and a generalized Dicke model describing many multi-level atoms coupled to a single cavity. We compare our theoretical predictions with recent QED experiments and point out the features of a counter-lasing transition. Our technique provides a convenient and powerful framework for analyzing driven-dissipative quantum systems, complementary to other approaches based on the solution of Lindblad master equations.

cond-mat.quant-gas↗

arXiv2019

Introduction to the Dicke model: from equilibrium to nonequilibrium, and vice versa

The Dicke model describes the coupling between a quantized cavity field and a large ensemble of two-level atoms. When the number of atoms tends to infinity, this model can undergo a transition to a superradiant phase, belonging to the mean-field Ising universality class. The superradiant transition was first predicted for atoms in thermal equilibrium and was recently realized with a quantum simulator made of atoms in an optical cavity, subject to both dissipation and driving. In this Progress Report, we offer an introduction to some theoretical concepts relevant to the Dicke model, reviewing the critical properties of the superradiant phase transition, and the distinction between equilibrium and nonequilibrium conditions. In addition, we explain the fundamental difference between the superradiant phase transition and the more common lasing transition. Our report mostly focuses on the steady states of atoms in single-mode optical cavities, but we also mention some aspects of real-time dynamics, as well as other quantum simulators, including superconducting qubits, trapped ions, and using spin-orbit coupling for cold atoms. These realizations differ in regard to whether they describe equilibrium or non-equilibrium systems.

quant-ph↗