Ignacio Cirac

Quantum Theory

Technical University Munich, Max Planck Institute of Quantum Optics

MPQ | Hans-Kopfermann-Str. 1

85748 Garching

Tel. +49 89 32905 736

ignacio.cirac[at]mpq.mpg.de

Group Webpage

What inspires me most about science is the possibility of learning something new every day.

Description

Research focus: quantum optics, quantum many body physics, quantum information

We carry out theoretical research in Quantum Optics, Quantum Information, and Quantum Many-Body Physics.

Quantum Optics

In Quantum Optics, we investigate how microscopic systems can be controlled and manipulated at the quantum level using external fields, and how such systems can be scaled up in a controlled way. We propose experiments that aim at observing interesting quantum phenomena, and develop specific theoretical tools for the problems at hand. We also develop proposals that use atomic systems for the quantum simulation of e.g. condensed matter or high energy physics models. The systems we explore include atoms in optical lattices, trapped ions, quantum dots, but also novel platforms (levitating spheres, nanoplasmonic lattices, NV-centers in diamond), hybrid systems and the use of engineered dissipation.

Quantum Information Theory

We also participate in the development of a theory of Quantum Information, which will be the basis of the applications in the world of communication and computation once microscopic systems can be controlled at the quantum level. This includes the study of the computational power of quantum computing, and which quantum states and computations can be simulated classically, but also the design of new quantum algorithms and quantum memories. In the field of quantum communication, we are concerned with the security of quantum key distribution schemes and the preparation of long-range entanglement, necessary for the construction of quantum networks. Our group also investigates questions related to Quantum Foundations, which aim at testing Quantum Mechanics itself. In particular we investigate macroscopic realism, as well as the possibilities of macroscopic superpositions.

Condensed Matter Physics

Another main research line consists of applying the ideas of Quantum Optics and Quantum Information to other disciplines, in particular to Condensed Matter Physics and the study of Quantum Many-Body Systems. A central tool are tensor networks, such as PEPS or MERA, with which we explore fermionic systems, mixed states, quantum field theories (with continuous MPS), and conformal field theories (with infinite MPS). We use them to theoretically characterize topological phases, classify the phases of matter, do renormalization group theory, establish a bulk-boundary correspondence and find parent Hamiltonians for states of interest. We also use them numerically to explore dynamical properties, anyonic excitations, and investigate High Energy Physics models. Finally, we also investigate phase diagrams of quantum spin models and analyze specific models.


Role within MCQST

Publications

Analogue quantum chemistry simulation

J. Argüello-Luengo, A. González-Tudela, T. Shi, P. Zoller & I. Cirac.

Nature 574, 215-218 (2019).

Show Abstract

Computing the electronic structure of molecules with high precision is a central challenge in the field of quantum chemistry. Despite the success of approximate methods, tackling this problem exactly with conventional computers remains a formidable task. Several theoretical and experimental attempts have been made to use quantum computers to solve chemistry problems, with early proof-of-principle realizations done digitally. An appealing alternative to the digital approach is analogue quantum simulation, which does not require a scalable quantum computer and has already been successfully applied to solve condensed matter physics problems. However, not all available or planned setups can be used for quantum chemistry problems, because it is not known how to engineer the required Coulomb interactions between them. Here we present an analogue approach to the simulation of quantum chemistry problems that relies on the careful combination of two technologies: ultracold atoms in optical lattices and cavity quantum electrodynamics. In the proposed simulator, fermionic atoms hopping in an optical potential play the role of electrons, additional optical potentials provide the nuclear attraction, and a single-spin excitation in a Mott insulator mediates the electronic Coulomb repulsion with the help of a cavity mode. We determine the operational conditions of the simulator and test it using a simple molecule. Our work opens up the possibility of efficiently computing the electronic structures of molecules with analogue quantum simulation.

DOI: 10.1038/s41586-019-1614-4

Time-dependent study of disordered models with infinite projected entangled pair states

C. Hubig, I. Cirac.

SciPost Physics 6, 031 (2019).

Show Abstract

Infinite projected entangled pair states (iPEPS), the tensor network ansatz for two-dimensional systems in the thermodynamic limit, already provide excellent results on ground-state quantities using either imaginary-time evolution or variational optimisation. Here, we show (i) the feasibility of real-time evolution in iPEPS to simulate the dynamics of an infinite system after a global quench and (ii) the application of disorder-averaging to obtain translationally invariant systems in the presence of disorder. To illustrate the approach, we study the short-time dynamics of the square lattice Heisenberg model in the presence of a bi-valued disorder field.

DOI: 10.21468/SciPostPhys.6.3.031

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