Research in Condensed Matter Physics
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter. It comprises the study of phenomena arising from the interactions of many particles, which give rise to the well-known solid, liquid and gas phases of matter, but also to plasmas, superconductors, Bose-Einstein condensates, and non-trivial-topology phases, among others.
Condensed Matter Physics is one of the broadest and most prolific subfields of Physics, since it brings together a wide range of systems and problems. However, all materials are ultimatedly made up of the same fundamental building blocks, so it is not the diversity in the basic constituents what leads to the most exotic and misterious phases of matter, but their aggregate behaviour and organization.
But how do complex phenomena emerge from these simple ingredients? Indeed, Condensed Matter Physics is all about understanding how the microscopic structure of a material connects with its macroscopic properties.
What do we do?
The main research lines of the group are devoted to the theoretical analysis of the electronic, topological and transport properties of low dimensional systems. We look for suitable platforms for quantum computation and quantum simulation.
Below are some of the topics where we focus our research and expertise:
- Quantum transport in quantum dot arrays and low dimensional systems:
- Long range charge, spin and qubit transfer at the nanoscale.
- Effect of hyperfine and spin orbit interactions: spin decoherence and relaxation.
- Quantum transport of strongly correlated electrons.
- Quantum charge and spin transfer in low dimensional systems with non trivial topology.
- Energy and heat transport in quantum dot arrays. Quantum engines.
- AC driven transport in nanostructures:
- Topological properties of ac driven systems at the nanoscale.
- Electron spin resonance in quantum dot arrays.
- Electronic properties of irradiated graphene
- Photoassisted long range charge, spin and qubit transport in nanostructures.
- Coupled quantum circuits
- Quantum charge detection and feedback in nanodevices.
- Majorana Fermions:
- Fractional Josephson effect.
- Floquet Majorana Fermions.
To learn more about the main topics, open the tabs below
The topological theory of matter has its roots in the 70s and 80s studies of polyacetylene, the quantum Hall effect, and superfluid 3He. The interest in the field exploded after the 2005 discovery of topological insulators. Crystalline solids exhibit a spectrum of energy bands constrained by the material's symmetries.
Topological properties of the band structure give rise to protected boundary states that are the hallmark of topological materials. Well-known examples include chiral and helical states in quantum (spin) Hall systems and Majorana modes in topological superconductors.
A central goal of research has become to identify systems with a topological spectrum. Theories of topological materials are often formulated with tight-binding models that describe hopping between localized electronic orbitals. This means that, given sufficient control, one can implement these models by assembling the corresponding structure from individual constituents that are suitably coupled.
Hence one may build "designer quantum materials" based on specific Hamiltonians through atomic assemblies. In fact recently the Su-Schrieffer-Hegger (SSH) model (a dimer chain) and the two-dimensional Lieb lattice have been implemented by STM techniques applied to vacancy defects in the c(2x2) chlorine superstructure on Cu(100). There are other examples such as photonic crystals, ultracold atomic gases trapped in optical lattices or coherent semiconductor devices and quantum dots which thanks to the impressive experimental advances have provided reliable and tunable setups to test and explore the intriguing topological properties of quantum systems.
Quantum dots are promising candidates for hosting qubits. The impressive control of these systems achieved in the last years not only allows one to host and manipulate charge and spin qubits in single and double quantum dots but also to implement longer arrays of quantum dots. Scaling up the quantum dot system is crucial for
realizing larger scale quantum gate operations and exploring multi- spin physics. To this end, spin qubit experiments with multiple quantum dots have been reported. In triple quantum dots (TQDs), spin blockade has been observed and an exchange-only qubit utilizing a TQD has been demonstrated. Experimental works have shown evidence of long-range transfer of electrons in arrays of three quantum dots in series. There, one particle is directly transmitted between distant dots without visiting the central región. This transfer occurs by means of virtual tunneling processes and the formation of coherent superpositions. where a single electron becomes delocalized between the left and right dot, while the middle dot remains empty. Therefore, both charge and spin are exchanged between the outermost dots. The delocalized electron acts as a quantum bus transferring the spin state from one end to the other. Other protocols, as coherent transfer by adiabatic passage combined with shortcuts to adiabaticity allow, as we showed in a recent work ,to transfer directly between edges two entangled electron spins Long range photoassisted tunneling has shown to be another mechanism
to transfer electrons directly between distant sites in quantum dot arrays. One of the main issues in spin qubits are spin decoherence and relaxation mechanisms. In GaAs quantum dots, hyperfine interaction is one of the main sources of electron spin relaxation. For that reason lateral quantum dots other materials as Si are actively
investigated. Silicon, can be isotopically purified and supports long spin lifetimes. It is therefore highly suited for spin qubit implementations. However, there is a main difference with respect to semiconductor III-V compounds, namely the valley degree of freedom. It stems from the six-fold degeneracy of the conduction band of bulk Si where in Si/SiGe heterostructures, the four in-plane valleys are raised in energy with respect to the two out-of-plane valleys through the strain in the Si quantum well. The relatively small energy splitting between the two low-lying valley states has been observed to contribute to spin relaxation, but may also be harnessed to make charge-noise-insensitive qubits. This valley splitting has been found to vary substantially within the range of 35–270 μeV in Si/SiGe QD devices. Other interesting candidates for qubits are spin hole qubits. Due to their wave function characteristics hyperfine interaction between nuclear and hole spins is very small. Therefore they are actively investigated not only in III-V compounds and Silicon but also in Germanium quantum dots.
Periodically driven quantum systems have been a fast-growing research field in recent years. The application of ac fields has become a very promising tool to engineer quantum systems.
The development of effective Hamiltonians describing ac driven systems at certain regimes has allowed us to predict novel properties such as topological phases and quantum phase transitions that otherwise would be
impossible to achieve in the undriven case. Floquet eigenstates and quasienergies are similar to eigenstates and energies of static systems, but the periodicity of the quasienergy spectrum introduces new features unique to periodically driven