arXiv subjects

Simon Panyella Pedersen

Publications and source records attributed to Simon Panyella Pedersen.

6 recordsLinked to original sources

arXiv2024

Green's function approach to interacting lattice polaritons and optical nonlinearities in subwavelength arrays of quantum emitters

Sub-wavelength arrays of quantum emitters offer an efficient free-space approach to coherent light-matter interfacing, using ultracold atoms or two-dimensional solid-state quantum materials. The combination of collectively suppressed photon-losses and emerging optical nonlinearities due to strong photon-coupling to mesoscopic numbers of emitters holds promise for generating nonclassical light and engineering effective interactions between freely propagating photons. While most studies have thus far relied on numerical simulations, we describe here a diagrammatic Green's function approach that permits analytical investigations of nonlinear processes. We illustrate the method by deriving a simple expression for the scattering matrix that describes photon-photon interactions in an extended two-dimensional array of quantum emitters, and reproduces the results of numerical simulations of coherently driven arrays. The approach yields intuitive insights into the nonlinear response of the system and offers a promising framework for a systematic development of a theory for interacting photons and many-body effects on collective radiance in two-dimensional arrays of quantum emitters.

cond-mat.quant-gas↗

arXiv2023

Nonlinear Quantum Optics in an Atomic Cavity

The idea of making photons effectively interact has attracted a lot of interest in recent years, for several reasons. Firstly, since photons do not naturally interact with each other, it is of fundamental physical interest to see what kind of medium can mediate interactions between these fundamental and non-interacting particles, and to what extent. Secondly, photonics is a major candidate for future quantum technology, due to the easy manipulation, readout, and transport of photons, which makes them ideal for quantum information processing. Finally, achieving strong and tunable interactions among photons would open up an avenue for exploring the many-body physics of a fluid of light. In this thesis, we will see how a cavity formed of subwavelength lattices of two-level atoms can confine photons to a nonlinear environment for a long time, such that emitted photons have accumulated strong correlations both among their momenta and in their temporal statistics. This speaks of a strong photon-photon interaction within the cavity. The nonlinearity originates in the saturability of individual atoms, and the lattice structure results in a strong and low-loss collective interaction with light. While a single atomic lattice has a largely linear nature, as the effect of individual atoms washes out in the collective response, the confining geometry of the cavity means the photons are exposed to the underlying saturability of the atoms for such a long time that the nonlinearity is revived. We will analyse this system both using a standard input-output formalism, where the nonlinear physics of the system is handled numerically, and a powerful Green's function-based approach that allows for exact analytical results with no additional approximations. This analytical description has the potential to lead to an exact study of the many-body physics of interacting photons in a two-dimensional setting.

quant-ph↗

arXiv2023

Quantum nonlinear metasurfaces from dual arrays of ultracold atoms

Atoms in a sub-wavelength lattices have remarkable optical properties that have become of high scientific and technological significance. Here, we show how the coupling of light to more than a single atomic array can expand these perspectives into the domain of quantum nonlinear optics. While a single array transmits and reflects light in a largely linear fashion, the combination of two arrays is found to induce strong photon-photon interactions that can convert an incoming classical beam into highly antibunched light. Such quantum metasurfaces open up new possibilities for coherently generating and manipulating nonclassical light, from optical quantum information processing to exploring quantum many-body phenomena in two-dimensional systems of strongly interacting photons.

quant-ph↗

arXiv2022

Dynamical quantum phase transitions in a noisy lattice gauge theory

Lattice gauge theories (LGTs) form an intriguing class of theories highly relevant to both high-energy particle physics and low-energy condensed matter physics with the rapid development of engineered quantum devices providing new tools to study e.g. dynamics of such theories. The massive Schwinger model is known to exhibit intricate properties of more complicated theories and has recently been shown to undergo dynamical quantum phase transitions out of equilibrium. With current technology, noise is inevitable and potentially fatal for a successful quantum simulation. This paper studies the dynamics subject to noise of a $(1+1)$D U$(1)$ quantum link model following a quench of the sign of the mass term. We find that not only is the system capable of handling noise at rates realistic in NISQ-era devices, promising the possiblity to study the target dynamics with current technology, but the effect of noise can be understood in terms of simple models. Specifically the gauge-breaking nature of bit-flip channels results in exponential dampening of state amplitudes, and thus observables, which does not affect the structures of interest. This is especially important as it demonstrates that the gauge theory can be successfully studied with devices that only exhibit approximate gauge invariance.

hep-lat↗

arXiv2021

Lattice gauge theory and dynamical quantum phase transitions using noisy intermediate scale quantum devices

Lattice gauge theories are a fascinating and rich class of theories relating to the most fundamental models of particle physics, and as experimental control on the quantum level increases there is a growing interest in non-equilibrium effects such as dynamical quantum phase transitions. To demonstrate how these physical theories can be accessed in near-term quantum devices, we study the dynamics of a (1+1)D U(1) quantum link model following quenches of its mass-term. We find that the system undergoes dynamical quantum phase transitions for all system sizes considered, even the smallest where the dynamics can be solved analytically. We devise a gauge invariant string order parameter whose zeros correlates with the structure of the Loschmidt amplitude, making the order parameter useful for experimental study in near-term devices. The zeros of the Loschmidt amplitude as well as the zeros of our order parameter are revealed by vortices in their phases, which can be counted by a topologically invariant winding number. With noisy intermediate scale quantum devices in mind, we propose a class of superconducting circuits for the general implementation of U(1) quantum link models. The principles of these circuits can be generalized to implement other, more complicated gauge symmetries. Furthermore, the circuit can be modularly scaled to any lattice configuration. Simulating the circuit dynamics with realistic circuit parameters we find that it implements the target dynamics with a steady average fidelity of $ 99.5\% $ or higher. Finally, we consider readout of the circuit using a method that yields information about all the degrees of freedom with resonators coupled dispersively to only a subset of them. This constitutes a direct and relatively straightforward protocol to access both Loschmidt amplitudes and the order parameter.

quant-ph↗

arXiv2019

Native three-body interaction in superconducting circuits

We show how a superconducting circuit consisting of three identical, non-linear oscillators in series considered in terms of its electrical modes can implement a strong, native three-body interaction among qubits. Because of strong interactions, part of the qubit-subspace is coupled to higher levels. The remaining qubit states can be used to implement a restricted Fredkin gate, which in turn implements a CNOT-gate or a spin transistor. Including non-symmetric contributions from couplings to ground and external control we alter the circuit slightly to compensate, and find average fidelities for our implementation of the above gates above $ 99.5\% $ with operation times on the order of a nanosecond. Additionally we show how to analytically include all orders of the cosine contributions from Josephson junctions to the Hamiltonian of a superconducting circuit.

cond-mat.supr-con↗