ML4Q Research

Scientific Structure

Following the mid-term review, the scientific program of ML4Q was restructured to span three focus areas, each addressing a specific set of problems relevant to the cluster’s mission. As part of the new structure, projects funded from 2023 onwards include research on NISQ computing and novel 2D materials.

Area A: Majorana devices and topological matter
(representative/deputy: Schäpers/Hassler)
Area B: NISQ and error-aware quantum computing
(representative/deputy: DiVincenzo/Müller)
Area C: Quantum networks and interconnects
(representative/deputy: Köhl/Bergschneider)

Core Projects

A1:

Materials, fabrications, and physics basis for topological-insulator Majorana devices

Majorana qubits will be built from topological-insulator (TI) nanowires and superconductors. In this core project, four work packages aim at the detection of the zero-bias conductance peak in TI-nanowire devices, the investigation of distinct Majorana signatures in circuit quantum electrodynamics (cQED) experiments with TI Josephson junctions (JJs), the understanding of disorder effects and the fabrication of TI-based JJ devices.

Participants

Ando (C)
Grützmacher (J)
Mussler (J)
Rosch (C)
Schäpers (J)
Schüffelgen (J)

Collaborators:
Blügel (J)
Hassler (A)
Mayer (J)
Moors (J)

Independence Grants:
Feng (C)
Schluck (C)

A2:

Quantum anomalous Hall insulator devices

This project aims to realize the promise of a proximitized QAHI (quantum anomalous Hall insulator) with the ultimate goal of demonstrating the braiding and realizing a flying Majorana qubit. We will work on developing basic tools and understanding of this platform, and we will try to confirm the chiral Majorana edge states.

Participants

Ando (C)
Bocquillon (C)
Egger (D)
Rosch (C)

Collaborators:
Blügel (J)
Hassler (A)

Open Call:
Dickel (C)
Rosenbach (C)

Independence Grants:
Feng (C)
Rosenbach (C)
Schluck (C)

A3:

Exploring Majorana modes in van der Waals heterostructures

This project sets out to explore the 2D material platform as host for Majorana zero modes and to evaluate their potential in the context of topological quantum computing. The project is based on the major recent progress in making tailored van der Waals heterostructures with very low intrinsic disorder potential in proximity of superconductors.

Participants

Bocquillon (C)
Hassler (A)
Morgenstern (A)
Stampfer (A)

Collaborators:
Kennes (A)

Open Call:
Rosenbach (C)

Independence Grants:
Rosenbach (C)

A4:

Ab-initio Bogoliubov-de Gennes investigation of superconducting interfaces for Majorana materials platforms

This project contributes to the characterization, understanding and control of the proximitized ordered and chemically disordered TI and QAHI and interfaces. We plan to study the decay of the proximity effect into topological materials, how the proximity
effect can be engineered from the local atomic structure and how disorder and intermixing at the interface affect the proximity effect.

Participants

Blügel (J)

Collaborators:
Ando (C)
Mayer (J)
Rosch (C)

Independence Grants:
Rüßmann (J/Würzburg)

A5:

Atomistic investigations of structure, chemistry and electronic properties in 3D TIs and at TI/SC interfaces

We carry out solid microstructural and structure-property relationship studies, aiming that our findings in multiple scales and multiple dimensions improve the fabrication of TI/SC with ideal interfaces and eventually lead to the realization of the desired Majorana systems.

Participants

Mayer (J)

Collaborators:
Ando (C)
Blügel (J)
Grützmacher (J)
Morgenstern (A)
Plucinski (J)
Stampfer (A)

A6:

Four-tip scanning tunneling microscope operating at 100 mK

This project aims to add a local perspective to quantum transport measurements by implementing the first-of-its-kind four-tip scanning tunneling microscope (4-tip STM) that operates below 100 mK with a 3D magnetic field of up to ~1 T. The abilities of the novel instrument are not restricted to Majorana physics and will enable tackling different questions related to other devices, such as superconducting qubits or spin qubits.

Participants

Balashov (A)
Morgenstern (A)

Collaborators:
Ando (C)
Lu (USC)
Mussler (J)Schüffelgen (J)
Stampfer (A)
Tautz (J)
Voigtländer (J)

Independence Grants:
Lüpke (J)

A7:

Majorana States and Parafermions in Ultracold Atom Systems

The aim of this project is to realize advanced topological quantum states, such as Majorana fermions and the computationally even more powerful parafermion (i.e. fractional Majorana) states, in cold atomic gas systems.

Participants

Köhl (B)
Kollath (B)
Rizzi (C)
Weitz (B)

Collaborators:
Diehl (C)
Rosch (C)

Open Call:
Schmitt (J)

B1:

Commissioning a NISQ platform: Enhancements and supremacy certification

We aim to develop new tools for mapping out the “computational phase diagram” – i.e. parameter regimes in which a new NISQ architecture is classically simulable, achieves “quantum supremacy”, or can be employed to solve useful problems beyond simulating itself. In addition, we want to enhance the computational utility of the Rydberg platform, by exploring non-standard ways to utilize this architecture.

Participants

Calarco (C/J)
Gross (C)
Hofferberth (B)
Luitz (B)

B2:

Disorder in quantum technology devices

The project addresses the effects of disorder in two of the most prominent platforms for future quantum information technology devices: the transmon qubit and its replication to medium scale computing platforms, and early device structures towards the realization of a Majorana qubit.

Participants

Altland (C)
Trebst (C)

Collaborators:
DiVincenzo (A/J)
Egger (D)
Hassler (A)

B3:

Fault-Tolerant Quantum Error Correction (QEC)

We will develop new fault-tolerant QEC strategies, noise mitigation, noise modelling and numerical simulation techniques, to explore QEC codes such as scalable topological codes, as well as quantum low-density parity check (qLDPC) codes, which offer highly promising alternatives to the “standard surface code” and for experimental realisations on NISQ devices.

Participants

Kennes (A)
Luitz (B)
Müller (A)
Trebst (C)
Wilhelm-Mauch (J)

Collaborators:
Bluhm (A)
Hofferberth (B)
Rizzi (C)

Open Call:
Rispler (A)

Independence Grants:
Rispler (A)

B4:

Measurement induced phase transitions on Rydberg NISQ devices

In a theory-experiment approach experimental signatures of measurement induced phase transitions (MITs) will be identified. We will use quantum feedback to single out one representative wave function from the random measurement trajectory ensemble. In first exploratory experiments, we will develop the building blocks for implementing quantum feedback operations in small Rydberg systems.

Participants

Altland (C)
Buchhold (C)
Diehl (C)
Hofferberth (B)

Collaborators:
Calarco (C/J)
Egger (D)
Müller (A)
Rizzi (C)

B5:

Quantum Software for the Near and Mid-Term

The project supports a broad set of activities that cover the major current trends in quantum algorithms that pertain to NISQ and early error-corrected architectures. In particular, compilers will be built that reduce the complexity of quantum circuits, first quantum chemical structure problems will be identified where a quantum advantage can be achieved on realistic NISQ hardware. Moreover, lower bounds for variational ansätze for combinatorial problems and the performance of quantum singular value transformation (QSVT) in the early fault-tolerant regime will be studied.

Participants

Berta (A)
Bruss (D)
Calarco/Wilhelm-Mauch (C/J)
Gogolin (Covestro)
Gross (C)

B6:

Robustness and controllability of driven open few and many-qubit ensembles

The project ranges from conceptual theoretical questions on the organizing principles of dissipative many body qubits and phase transitions, the self-organization with quantum light and qubits, to the topological quantization in mixed quantum states including under non-equilibrium conditions. This is complemented with the experimental exploration of the generation of well controlled entangled qubit states in programmable quantum simulators.

Participants

Diehl (C)
Köhl (B)
Kollath (B)

Collaborators:
Altland (C)
DiVincenzo (A/J)
Egger (D)
Müller (A)
Rosch (C)
Schmitt (B)
Weitz (B)

C1:

Telecom-ready optical interface to qubits in gate-defined quantum dots with high coupling efficiency

This project bridges the two domains of electrically controlled qubits in gated defined quantum dots and optically controlled spins in self-assembled dots by realizing an optical quantum interface for qubits in gate-defined quantum dots, building on the GaAs platform. The goal is to use this interface to achieve a quantum connection to ion qubits, by building on the capabilities of wavelength conversion and innovative methods to reach a high photon coupling efficiency already developed during the first years of funding.

Participants

Bluhm (A)
Kardynal (J)
Wieck (RU Bochum)

Collaborators:
Elsen/Jungbluth (ILT Aachen)
Ludwig (RU Bochum)
Witzens (A)

C2:

Optical coupling of qubits in 2D materials

We will assess a potentially scalable quantum technology platform based on 2D materials that does not only contain long-coherence qubits but also incorporates an integrated photonic interface realized by coupled quantum emitters in a cavity. The coupling of several quantum emitters to the same cavity mode will enable beyond-nearest-neighbor and beyond-two-qubit operations.

Participants

Bergschneider (B)
Kennes (A)
Kurzmann (A)
Stampfer (A)
Viola Kusminskiy (A)

Collaborators:
Blügel (J)
Kardynal (J)
Köhl (B)
Linden (B)
Waldecker (A)

C3:

Multipartite quantum networks

What type of novel quantum protocols can be used on quantum networks involving several nodes? We continue to theoretically develop key concepts for quantum networking in multipartite architectures, as well as to experimentally push corresponding implementations with highly entangled photon states. The general idea here is that the use of suitable highly entangled resource states can speed up multipartite quantum connectivity.

Participants

Kroha (B)
Murta (D)
Schmitt (B)
Weitz (B)

Collaborators:
Bruss (D)
Gross (C)
Grützmacher (J)
Kampermann (D)

Open Call:
Pawlis (J)

Independence Grants:
Ferreri (J)
Grasselli (D)

C4:

A quantum link between a solid-state emitter and an atomic qubit

Scalable quantum computers will require interfaces that can distribute entangled states over macroscopic distances. We will demonstrate such interfaces and develop a small hybrid quantum network consisting of a quantum dot coupled to a trapped ion in an optical cavity. The trapped ion which constitutes the quantum memory offers excellent coherence times and has proven to be a quantum network node with very high fidelity. On the contrary, the solid state emitter constituted by a quantum dot in InGaAs offers very fast manipulation and high photon emission rates, as well as the potential to be coupled to scalable qubits.

Participants

Kardynal (J)
Köhl (B)
Linden (B)
Stellmer (B)

Open Call:
Witzens (A)

Independence Grants:
Rani (J)

C5:

Electron shuttling for scalable semiconductor quantum computing

To realize topological error correction one needs reliable building blocks connected by quantum links. We continue our work on the quantum bus to shuttle spin qubits over micron-scale distances. We focus on spin coherence during shuttling and will experimentally realize a “quantum Turing machine”, which promises multi-qubit capabilities with a limited complexity in a very elegant manner and at the same time is well-suited to demonstrate the potential of a shuttling-based architecture.

Participants

Bluhm/Schreiber (A)
DiVincenzo (A/J)

Collaborators:
Knoch (J)
Motzoi/Calarco (C/J)

Independence Grants:
Sala (A)