News

New Editors’ Suggestion: Proposal for Detection of the 0′ and π′ Phases in Quantum-Dot Josephson Junctions

We are pleased to announce our latest article and thank the APS for considering it an Editors’ Suggestion on PRL. Congrats, everyone!
Minchul Lee, Rosa López, H. Q. Xu, and Gloria Platero
Phys. Rev. Lett. 129, 207701
The competition between the Kondo correlation and superconductivity in quantum-dot Josephson junctions (QDJJs) has been known to drive a quantum phase transition between 0 and π junctions. Theoretical studies so far have predicted that under strong Coulomb correlations the 0π transition should go through intermediate states, 0 and π phases. By combining a nonperturbative numerical method and the resistively shunted
junction model, we investigated the magnetic-field-driven phase transition of the QDJJs in the Kondo regime and found that the low-field magnetotransport exhibits a unique feature which can be used to distinguish the intermediate phases. In particular, the magnetic-field driven ππ transition is found to lead to the enhancement of the supercurrent which is strongly related to the Kondo effect.
Figure 1

Group Seminar: Controlling Topological Phases of Matter with Quantum Light

Olesia Dmytruk, from the CNRS, Collège de France, PSL Research University, Paris

Date: November 22, 2022, 12:00h

Location: Instituto de Ciencias de Materiales de Madrid (ICMM-CSIC), Salón de Actos

Abstract:

Controlling the topological properties of quantum matter is a major goal of condensed matter physics. A major effort in this direction has been devoted to using classical light in the form of Floquet drives to manipulate and induce states with non-trivial topology. A different route can be achieved with cavity photons. In this talk, I will discuss a prototypical model for topological phase transition, the one-dimensional Su-Schrieffer-Heeger (SSH) model, coupled to a single mode cavity [1]. I will demonstrate that quantum light can affect the topological properties of the system, including the finite-length energy spectrum hosting edge modes and the topological phase diagram. In particular, I will show that depending on the lattice geometry and the strength of light-matter coupling one can either turn a trivial phase into a topological one or vice versa using quantum cavity fields. Furthermore, the polariton spectrum of the coupled electron-photon system contains signatures of the topological phase transition in the SSH model.


References:

[1] Olesia Dmytruk and Marco Schiró, Controlling topological phases of matter with quantum light, arXiv:2204.05922.

Group Seminar: Illuminating van der Waals materials: from graphene to twisted MoS2

Marta Prada, from the Institute for Theoretical Physics, Universität Hamburg, will give a seminar entitled «Illuminating van der Waals materials: from graphene to twisted MoS2».

Date: October 11th, 2022, 11:00h.

Location: Instituto de Ciencias Materiales de Madrid (ICMM-CSIC)

We address the low-lying energy levels of van-der Waals structures via resistively-detected electron spin resonance (ESR). In graphene, the structure of the topological bands is reflected in transport experiments, where our numerical models allow us to identify the resonance signatures. We resolve the intrinsic spin-orbit gap [1], the g-factor anisotropic corrections [2, 3], the sub-lattice splitting [4], and the hyperfine-induced splitting in 13C-based graphene [5]. Using Floquet formalism, we find theoretical evidence of a topological transition by illuminating an ideal sample of graphene and the connection between angular momentum and sublattice spin. Finally, we study twisted MoS2 samples, where we resolve low-lying Moiré bands near the conduction band.

Keywords: Twisted bilayer MoS2, Moiré, superlattices, Mini-bands, Schottky barrier, Resonant Tunneling,
Transition metal dichalcogenides

[1] J. Sichau, M. Prada, T. Anlauf, T. J. Lyon, B. Bosnjak, L. Tiemann, and R. H. Blick, Phys. Rev. Lett. 122, 046402 (2019).
[2] M. Prada, L. Tiemann, J. Sichau and R. H. Blick. Phys. Rev. B 104, 075401 (2021).
[3] M. Prada, Phys. Rev. B 103, 115425 (2021).
[4] R. Singh, M. Prada, V. Strenzke, B. Bosnjak, T. Schmirander, Lars Tiemann, and Robert H. Blick. Phys. Rev. B 102, 245134 (2020).
[5] V. Strenzke, Phys. Rev. B 105, 144303 (2022).

Seminar: «Introduction to machine learning and its applications in scientific research

Lamberto Oltra Nieto, a member of our group, will give a seminar entitled «Introduction to machine learning and its applications in scientific research».

Date: March 9th, 2022, 10:00 h.

Location: online

Abstract: Nowadays, the importance of new technologies, more specifically artificial intelligence, in science is undeniable and must be taken into account in new scientific research. This seminar aims to be an introduction to the basics of machine learning with the objective of highlighting this importance in research. Applications in various fields such as error correction in different quantum systems or material research will also be discussed.

Seminar: «Hole spin qubits in elongated quantum dots»

Mónica Benito, from the Institute of Quantum Technologies, German Aerospace Center (DLR), Ulm, will give a seminar entitled «Hole spin qubits in elongated quantum dots».

Date: March 9th, 2022, 11:00 h.

Location: Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC)

Abstract: Rapid development has positioned quantum wells in planar germanium heterostructures at the head of semiconductor quantum dot platforms for quantum information processing [1,2]. We find nuclear-spin-free isotopes, low charge noise and low disorder. The focus is on hole states, due to the absence of valley states, a technically advantageous low effective mass, and the strong spin-orbit coupling that allows for all-electric operation. These works employ heavy-hole spin qubits, which constitute the ground states in these planar devices. Theory predicts an even more promising future for germanium and/or silicon based quantum dots fabricated in nanowires, based on tunable and even stronger spin-orbit coupling relying on the high degree of heavy-light hole mixtures [3]. I will present recent theoretical efforts to understand and experimentally identify the low-energy physics of hole germanium nanowires, including the effect of orbital effects of the magnetic field [4]. We predict optimal qubit operation at a sweet spot with Rabi frequencies in the GHz regime. We find that they can present strong and tunable spin-orbit coupling if the confinement potential is properly squeezed [5]. This confinement-induced spin-orbit coupling, and therefore the qubit-resonator coupling, could be turned on and off, overcoming present scalability challenges.
[1] Hendrickx et al., Nature 591, 580 (2021)
[2] F. van Riggelen, et al., arXiv:2202.11530
[3] C. Kloeffel, et al., Phys. Rev. B 84, 195314 (2011)
[4] C. Adelsberger, M. Benito, S. Bosco, J. Klinovaja, and D. Loss, PRB 105, 075308 (2022)
[5] S. Bosco, M. Benito, C. Adelsberger, and D. Loss, PRB 104, 115425 (2021)

Seminar: «Entanglement generation and simulation of relativistic effects with parametric oscillators in cQED»

David Fernández, from Instituto de Física Fundamental (IFF-CSIC), will give a seminar entitled «Entanglement generation and simulation of relativistic effects with parametric oscillators in cQED».

Date: February 23rd, 2022, 11:00 h.

Location: Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC)

Abstract: Present day quantum technologies aim at building quantum computers and networks that outperform their classical counterparts. From a physical perspective, these technologies need to be systems whose parameters are modified in real time, so that a programable sequence of operations is performed to deliver different quantum applications. Then, it is only natural to consider parametric oscillators as a primitive for these devices. In this seminar, we will discuss the basics of parametric oscillators in superconducting circuits and their applications to two promising topics: Firstly, the generation of multipartite entanglement thanks to the parametric amplification of vacuum in microwave one-dimensional cavities. Additionally, we will introduce protocols for the detection of said entanglement, which lead to connections in open questions in quantum information theory. Secondly, we will present superconducting circuits designed for the analog simulation of relativistic phenomena such as the Unruh and dynamical Casimir effects.

Open PostDoc Position: «Quantum processors in semiconductor quantum dots platforms: Theoretical modelling for new quantum functionalities»

Dear colleague,

I would like to bring to your attention to the following open postdoc position: “Quantum processors in semiconductor quantum dots platforms: Theoretical modelling for
new quantum functionalities”. Our theoretical group: “Novel Platforms and Nano-devices for Quantum Simulation and Computation”, at the Materials Science Institute of Madrid(ICMM), located at the Campus of Excellence of the Autonomous University-CSIC, is seeking well-qualified, highly motivated, and dynamic young scientists at post-doc level in the area of transport in semiconductor quantum dot arrays for quantum information transfer and quantum simulation. The contract is funded by the Spanish National Research Council (CSIC) within the newly-established platform PTI+ on QuantumTechnologies, a virtual cluster of more than 30 CSIC groups sharing a common vision in Quantum Science and Technology.

We seek a person with experience in condensed matter theory, including solid state qubits and quantum transport. Experience in solid state qubits- quantum cavities hybrid systems and in topological low dimensional systems will be valued positively. Also, experience in Machine Learning for quantum information tasks is a plus. Close collaboration with state of the art experimental labs is expected.

The position is funded for two years. If you are interested, please send your questions for
further details to Prof. Gloria Platero: gplatero@icmm.csic.es. Possible candidates should
provide a curriculum vitae, a brief letter of motivation, a summary of their research
experience, and a list of publications. Two reference letters should be arranged to be sent
directly to the email above.

Group Seminar: «Hole spin qubits manipulation with shortcuts to adiabaticity protocols», David Fernández

David Fernández, a MSC student in our group, will give a seminar entitled «Hole spin qubits manipulation with shortcuts to adiabaticity protocols», as part of the group seminars.

Date: June 8th, 2021, 10:30 h.

Location: online

Abstract: Hole spins in semiconductor QDs are also attracting significant attention as candidates for fast, highly co-
herent, spin qubits. They have long coherence time due to the weak hyperfine coupling to nuclear spins , and have demonstrated to have rapid operation times due to the inherently strong spin–orbit coupling (SOC), which also allows spin states to be controlled locally with electric fields applied to the gate electrodes.
Recently, Landau Zener Stückelberg Majorana spectroscopy on two-hole GaAs double quantum dot has been experimentally implemented. Motivated by these experiments, we investigate how to control and manipulate a spin qubit consisting on a triplet and a singlet hole state, by alternative driving protocols which reduce the otherwise unavoidable presence of charge noise. Shortcuts to adiabaticity (STA) are a set of techniques to reduce the duration of slow adiabatic processes, minimizing noise effects while keeping or enhancing robustness. Different driving protocols have been developed, which reduce the time of the process below characteristic decoherence times. Here we will consider the fast quasi-adiabatic (FAQUAD) approach and we will analyze its feasibility to manipulate hole spin qubits and compare with other alternative protocols.

Thesis Defense: «Quantum dynamics in low-dimensional topological systems»

On January 30th, we attended the Thesis Defense of one of our PhD students, Miguel Bello, entitled «Quantum dynamics in low-dimensional topological systems»

Abstract: The discovery of topological matter has revolutionized the field of condensed matter physics giving rise to many interesting phenomena, and fostering the development of new quantum technologies. In this thesis we study the quantum dynamics that take place in low dimensional topological systems, specifically 1D and 2D lattices that are instances of topological insulators. First, we study the dynamics of doublons, bound states of two fermions that appear in systems with strong Hubbard-like interactions. We also include the effect of periodic drivings and investigate how the interplay between interaction and driving produces novel phenomena. Prominent among these are the disappearance of topological edge states in the SSH-Hubbard model, the sublattice confinement of  doublons in certain 2D lattices, and the long-range transfer of doublons between the edges of any finite lattice. Then, we apply our insights about topological  insulators to a rather different setup: quantum emitters coupled to the photonic analogue of the SSH model. In this setup we compute the dynamics of the emitters, regarding the photonic SSH model as a collective structured bath. We find that the topological nature of the bath reflects itself in the photon bound states and the effective dipolar interactions between the emitters. Also, the topology of the bath affects the single-photon scattering properties. Finally, we peek into the 
possibility of using these kinde of setups for the simulation of spin Hamiltonians and discuss the different ground states that the system supports.

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