Quantum field theory can be used to describe continuous bosonic systems with infinitely many degrees of freedom, each with infinite local Hilbert space dimensions. Traditionally, this has made the study of these systems difficult beyond the Gaussian regimes or perturbative regimes, except in one-dimensional systems where some powerful numerical and analytical techniques are available. In particular, it is often hard to make statements directly in the continuum, such as the entanglement structure of the states or operators. Recently some progress has been made in this direction using tools from tensor network theory.

Selected publications:

• ET, J. I. Cirac, Continuous matrix product operators for quantum fields (arXiv 2025) 

Relativistic quantum fields are highly constrained in that it has exact causal structure (microcausality): two observers at spacelike separation cannot, through the use of quantum fields, signal to one another and perform superluminal signaling, even if the field states has large amount of (vacuum) entanglement. Two natural questions arise from the interplay between signaling and vacuum entanglement, namely 

(i) how well the vacuum entanglement can be used to transmit (classical/quantum) information between two local observers interacting locally with the field, and 

(ii) whether one can in principle extract vacuum entanglement using localized probes and how it is influenced by relativistic causality.

Selected publications:

• K. Gallock-Yoshimura, ET, Bipartite and tripartite entanglement in pure dephasing relativistic spin-boson model (PRD 2025)

• M. Kasprzak, ET, Transmission of quantum information through quantum fields in curved spacetimes (JPA 2025)

• ET, K. Gallock-Yoshimura, Channel capacity of relativistic quantum communication with rapid interaction (PRD 2022)

• F. Gray, D. Kubizňák, T. May, S. Timmerman, ET, Quantum imprints of gravitational shockwaves (JHEP 2021)

• ET, E. Martín-Martínez, When entanglement harvesting is not really harvesting (PRD 2021)

• ET, R. B. Mann, Harvesting correlations in Schwarzschild and collapsing shell spacetimes (JHEP 2020)

• ET, E. Martín-Martínez, Zero mode suppression of superluminal signals in light-matter interactions (PRD 2019)

My first entry to physics in undergraduate studies was through black hole chemistry --- the idea that one can extend the laws of black hole thermodynamics by interpreting cosmological constant as a thermodynamic variable, namely the pressure term. This leads to various surprising connection between classical thermodynamics and black hole physics, such as the formal equivalence between the "equation of state" for black holes with those of van der Waals fluid and we found the first example that exhibits the "lambda" transition seen in superfluid systems.

Selected publications:

• Robie A. Hennigar, R. B. Mann, ET, Superfluid Black Holes (PRL 2017)

• R. A. Hennigar, ET, R. B. Mann, Thermodynamics of hairy black holes in Lovelock gravity (JHEP 2017)