Friday Quantum Seminar

Quantum sensing leverages the principles of quantum mechanics to provide ``quantum-enhanced'' measurement sensitivity, thereby amplifying our ability to observe interesting physical phenomena. It employs a rich arsenal of techniques, including squeezing, photon counting, entanglement assistance, and distributed quantum sensing to achieve unprecedented sensitivity.

D. Carney et al. [https://doi.org/10.1103/PRXQuantum.2.030330] suggest the use of a trapped atom interferometer combined with a mechanical oscillator to test certain theories combining quantum mechanics with gravity. We construct an entanglement witness applicable to the stated interferometer-oscillator setup. We also investigate the effects of atomic dephasing and thermal noise on the practical use of this entanglement witness in an experimental implementation of such a system.

We address the question of whether open quantum system dynamics which host mixed symmetry-protected topological (SPT) states as steady states continue to do so after introducing symmetric perturbations. In particular, we discuss the characteristics of the decohered cluster state --- a mixed SPT protected by a combined strong and weak symmetry --- and construct a parent Lindbladian which hosts it as a steady state. The parent Lindbladian can be mapped onto reaction-diffusion dynamics, which is exactly solvable, even in the presence of certain perturbations.

Extensively degenerate ground-state spaces due to frustration pose a formidable resource for emergent quantum phenomena. Perturbing extensively degenerate ground-state spaces may result in several distinct scenarios lifting the ground-state degeneracy. First, an infinitesimal perturbation can lead to a symmetry-broken order (order-by-disorder) or second the perturbation can result in a symmetry-unbroken phase (disorder-by-disorder), which can be either trivial or an exotic quantum spin liquid.

Quantum confinement significantly influences the excited states of sub-10 nm single-walled carbon nanotubes (SWCNTs), crucial for advancements in transistor technology and the development of novel opto-electronic materials such as fluorescent ultrashort nanotubes (FUNs). However, the length dependence of this effect in ultrashort SWCNTs is not yet fully understood in the context of the SWCNT exciton states.

Quantum error correction protects logical quantum information against environmental decoherence by encoding logical qubits into entangled states of physical qubits. One of the most important near-term challenges in building a scalable quantum computer is to reach the break-even point, where logical quantum circuits on error-corrected qubits achieve higher fidelity than equivalent circuits on uncorrected physical qubits.

We define a quantum monomer-dimer model on a Penrose tiling (a quasicrystal) in the space of maximal dimer coverings. Monomers are necessarily present because it was shown by F. Flicker et al., PRX 10, 011005 (2020) that there are no perfect dimer coverings of Penrose tilings. Despite the presence of a finite density of monomers, our model has a Rokhsar-Kivelson (RK) point at which the ground state is a uniform superposition of all maximal dimer coverings.

Antiferromagnetic materials with microscopic behavior resembling that of the Fermi-Hubbard model are expected to host excitons, or bound electron-hole pairs. In order to investigate such behavior, we have optimized states of the t-J model in the single-particle-single-hole sector using the density matrix renormalization group (DMRG).

The intersection of quantum electrodynamics (QED) and density-functional theory (DFT) has opened up exciting opportunities in controlling quantum matter through light-matter coupling. This frontier, however, is beset with computational challenges, especially in the weak and strong coupling regimes. Building upon previous research, we present the results of nonperturbative QED functional in the long-wavelength limit, centered solely on the matter Hilbert space.

Topological band structures are well known to produce symmetry-protected chiral edge states which transport particles unidirectionally. These same effects can be harnessed in the frequency domain using a spin-1/2 system subject to periodic drives.