# Schedule

#### Sunday

**13:00 – 18:30**

#### Hike

**Meeting point:** Central station.**Fee:** free

We kick off the school with a short hike to the historic castle *Haut-Barr*. The bus will leave at 13:00, so better be on time.

Credits: https://www.alsaceterredechateaux.com/de/burgen-und-befestigte-staedte/hohbarr-haut-barr/

**19:30 – 22:00**

#### Welcome reception

**Location**: National library**Fee:** free

The welcome reception at the Strasbourg national library will be the official opening of the spring school. After the welcome talk you will have the opportunity to meet the other participants and enjoy small aperitifs and drinks.

#### Monday

**8:00 – 8:30**

**Arrival**

**8:30 – 9:00**

#### Opening

**Location**: ISIS building, Esplanade campus.**Fee:** free

**9:00-10:30**

#### Introductory lectures

**Location**: ISIS building, Esplanade campus.

#### 9:00 – 9:45 **Prof. Immanuel Bloch**

*(MPQ & Ludwig-Maximilians-Universität, DE)*

##### Quantum Simulations using Ultracold Atoms in Optical Lattices

More than 30 years ago, Richard Feynman outlined his vision of a quantum simulator for carrying out complex calculations on physical problems. Today, his dream is a reality in laboratories around the world. In these lectures, I will give an introduction to quantum simulations using ultracold atoms trapped in optical lattices. We will cover basic cooling, trapping, manipulation and detection mechanisms for these systems including Quantum Gas Microscopes, which allow for single atom resolved detection with single lattice site resolution. In the second part of the lecture, I will outline a few applications regarding quantum simulations of condensed matter systems, namely the Fermi Hubbard model, which plays an essential role in the context of High-Tc superconductivity, experiments on new dynamical phases of matter, as well as topological systems.

#### 9:45 – 10:30 **Prof. Thomas Ebbesen**

*(ISIS, University of Strasbourg, FR)*

##### The alchemy of vacuum

Over the past decade, there has been a surge of interest in the ability of hybrid light-matter states to control the properties of matter and chemical reactivity. Such hybrid states can be generated by simply placing a material in the spatially confined electromagnetic field of an optical resonator, such as that provided by two parallel mirrors. This occurs even in the dark because it is electromagnetic fluctuations of the cavity (the vacuum field) that strongly couple with the material. Experimental and theoretical studies have shown that the mere presence of these hybrid states can enhance properties such as transport, ferromagnetism, and superconductivity and modify (bio)chemical reactivity. This emerging field is highly multidisciplinary, and much of its potential has yet to be explored. In this lecture, this topic will be introduced together with some of the experimental and theoretical challenges.

For a review on the topic please see: Garcia-Vidal, Ciuti, Ebbesen, Science 373, eabd0336 (2021)

**10:30 – 11:00**

#### Coffee break

**11:00 – 12:30**

#### Student talks

**Location**: ISIS building, Esplanade campus.

#### Liam Bond

*(University of Amsterdam)*

**Quantum Simulation with Trapped Ions in Optical Tweezers**

Trapped ions are one of the most advanced platforms for digital and analogue quantum simulation. A suitable ion species such as Yb+ has an internal structure suitable for cooling, initialising, and read-out. These properties, together with long coherence times, have resulted in the highest fidelity two-qubit gates, an essential element for digital quantum simulation. However, analogue quantum simulators may enable more efficient simulation of certain Hamiltonians.

In analogue quantum simulators, qubit interactions are mediated by the Coulomb crystal’s collective vibrations and are thus natively long ranged. However, controlling the interactions remains challenging. We can use optical tweezers, which add a small, tuneable harmonic potential to each ion, to gain more control. I will introduce this proposal and our simulations of experimental effects: micromotion, local stress and intensity noise [1,2]. We find that these effects can be easily circumvented when designing appropriate tweezer patterns.

[1] Arias Espinoza et al., “Engineering spin-spin interactions with optical tweezers in trapped ions”, Phys Rev A 104, 013302 (2021)

[2] Bond et al., “The Effect of Micromotion and Local Stress in Quantum simulation with Trapped Ions in Optical Tweezers“, arXiv:2202.13681 (2022)

#### Lucille Caussou

*(INSP – Sorbonne Université)*

**Interlayer Excitons in MoSe2-WSe2 Heterobilayers**

Transition Metal Dichalcogenides (TMDs) monolayers are semiconductors hosting strongly bound electron-hole pairs, i.e. excitons, that are remarkably possibly studied up to room temperature. When two distinct monolayers are stacked onto each other, realizing a so-called hetero-bilayer, a periodic bandgap modulation spontaneously forms. Electronic carriers are then confined in an hexagonal lattice potential with nanometric dimensions and tunable depth. This potential is referred to as moiré potential. Here I report experiments probing interlayer excitons, made by the Coulomb attraction between electrons confined in a MoSe2 monolayer and holes in the adjacent WSe2 monolayer, at low temperature (4K). Then, I emphasize the spectroscopic signatures of interlayer excitons, and discuss the role of the moiré potential relying on polarisation resolved spectroscopy. I finally discuss the potential of our studies to explore the physics of the Bose-Hubbard model.

#### Nikolas Liebster

*(Heidelberg University)*

**Quantum Field Simulator for Dynamics in Curved Space times**

The observed large-scale structure in our Universe is seen as a result of quantum fluctuations amplified by spacetime evolution. This, and related problems in cosmology, asks for an understanding of the quantum fields of the standard model and dark matter in curved spacetime. Even the reduced problem of a scalar quantum field in an explicitly time-dependent spacetime metric is a theoretical challenge and thus a quantum field simulator can lead to new insights. Here, we demonstrate such a quantum field simulator in a two-dimensional Bose-Einstein condensate with a configurable trap and adjustable interaction strength to implement this model system. We explicitly show the realisation of spacetimes with positive and negative spatial curvature by wave packet propagation and confirm particle pair production in controlled power-law expansion of space. We find quantitative agreement with new analytical predictions for different curvatures in time and space. This benchmarks and thereby establishes a quantum field simulator of a new class. In the future, straightforward upgrades offer the possibility to enter new, so far unexplored, regimes that give further insight into relativistic quantum field dynamics.

#### Carmen Blaas-Anselmi

*(Università degli Studi di Milano Statale – Université de Strasbourg)*

**Asymmetric power dissipation in electronic transport through a quantum point contact**

The understanding of electronic transport through nanostructures is crucial for the development of modern electronic devices. Moreover, the subject is of fundamental interest due to the presence of quantum coherent processes and its position at the frontier between classical and quantum physics. While traditional transport experiments measure the conductance and its dependence on parameters like an applied magnetic field, a recently developed nanothermometry technique is able to detect heat production on the surface of a sample with incredibly high spatial resolution, indicating where dissipation occurs in electronic quantum transport through a two-dimensional electron gas. The aim of this research was to start investigating the power dissipation of an electronic current flowing through a QPC in a 2DEG. Based on the Landauer-Büttiker approach, the power dissipated on the two sides of the narrow constriction is studied as a function of temperature, applied voltage and mean electrochemical potential. We demonstrated that an asymmetry appears in the dissipation, which is most pronounced when the quantum point contact is tuned to a conductance step where the transmission strongly depends on energy. At low temperatures, the asymmetry is enhanced when the temperature increases.

C. Blaas-Anselmi, F. Helluin, R. A. Jalabert, G. Weick, D. Weinmann, Asymmetric power dissipation in electronic transport through a quantum point contact, SciPost Phys. 12, 105 (2022)

#### Shuzhe Yang

*(Université de Strasbourg)*

**Microwave electric field sensing with cold Rydberg atoms**

The atom-based traceable standard for microwave electrometry shows promising advantages by enabling stable and uniform measurement. Possessing transitions from gigahertz to terahertz, Rydberg atoms systems have been utilized to develop quantum technology such as microwave electrometry[1,2], microwave to optics conversion[3] and so on. Here we theoretically propose and then experimentally realize an alternative direct International System of Units (SI)–traceable and self-calibrated method for measuring a microwave electric-field strength based on electromagnetically induced absorption (EIA) in cold Rydberg atoms. Comparing with the method of electromagnetically induced transparency, EIA measurement method is more valid and is even more robust against the experimental parameters, which enables us to realize a direct SI-traceable microwave-electric-fifield measurement as small as ∼100 μV/cm[1].

[1] K.-Y. Liao, H.-T. Tu, S.-Z. Yang et al., “Microwave electrometry via electromagnetically induced absorption in cold rydberg atoms,” Physical Review A 101,053432 (2020).

[2] J. A. Sedlacek, A. Schwettmann, H. Küblerwet et al., “Microwave electrometry with rydberg atoms in a vapour cell using bright atomic resonances,” Nature Physics 8, 819–824 (2012).

[3] H.-T. Tu, K.-Y Liao, Z.-X Zhang, X.-H Liu, S.-Y Zheng, S-Z Yang et al., ”High-efficiency coherent microwave-to-optics conversion via off-resonant scattering”, Nature Photonics (2022).

**12:30 – 14:00**

#### Lunch

**Location**: CROUS Resto’U Paul Appel**Cost:** free

We will have lunch together at Crous.

**14:00 – 15:30**

#### Introductory lectures

**Location**: ISIS building, Esplanade campus.

#### 14:00 – 14:45 **Prof. Stéphane Berciaud**

*(IPCMS, University of Strasbourg, FR)*

##### Introducing quantum two-dimensional materials

The quest for low-dimensional systems with novel quantum properties is one of the most active research efforts in materials science. In this context, two-dimensional (2D) materials (such as mono of few-layers of graphene, boron nitride, transition metal dichalcogenides or magnetic layered materials) compose a broad palette of atomically-thin crystals with remarkable electronic, optical, spin, valley and even mechanical properties. These assets can be enhanced *ad lib* by stacking 2D layers into so-called van der Waals heterostructures and thereby tailoring novel functionalities and devices that cannot be achieved using more conventional materials and low-dimensional heterostructures.

These two lectures aim at introducing 2D materials and some of their peculiar quantum properties. The first lecture will introduce the physics of some of the most popular 2D systems (namely graphene and atomically-thin semiconductors) and selection of landmark experiments, presented with a “historical” perspective. The second lecture will focus on van der Waals engineering, explaining how exquisite control of the stacking sequence, nanoscale environment and rotational mismatch (the so-called twist angle) have recently led to beautiful discoveries with outcomes for quantum photonics and (opto-)electronics.

Selected recent reviews:

A. H. Castro Neto *et al.*, “The electronic properties of graphene”, *Rev. Mod. Phys.* **81**, 109 (2009)

G. Wang *et al.*, “Colloquium: Excitons in atomically thin transition metal dichalcogenides”, *Rev. Mod. Phys. ***90**, 021001 (2018)

N. Wilson *et al.*, “Excitons and emergent quantum phenomena in stacked 2D semiconductors”, *Nature* **599**, 383 (2021)

#### 14:45- 15:30 **Dr. Fabian Steinlechner **

*(Fraunhofer IOF, DE)*

##### Quantum Communication in space

**15:30 – 16:00**

#### Coffee break

**16:00 – 18:00**

#### Transferable skills courses

**Location**: ISIS building, Esplanade campus.

The soft skills courses allow you to build a valuable toolbox that extends beyond your scientific expertise. You may choose between either of the two.

#### Science communication

Efficiently communicating your scientific results to others is an important skill for raising awareness among the general public, but is also inevitable for a successful funding application. This course, which will be taught by the experts from *Science Birds*, will help you improve these important communication skills.

#### Innovation training

*What is innovation and how do you boost your innovativeness?*

Our experts from SATT will give you a crash course in innovation, which will be complemented by an interactive panel discussion.

**18:30 – 20:00**

#### City tour

**Location:** Docks.**Fee:** free

Strasbourg is a beautiful city at the heart of Europe and it would be a shame to leave it unexplored during this spring school. Since all major sights can be seen from the water, we will take a Batorama boat tour on Strasbourg’s charming canals. The boat will leave at 18:30 sharp!

image credits: visit.alsace

#### Tuesday

**9:00-10:30**

#### In-depth lectures

**Location**: ISIS building, Esplanade campus.

Courses will be given in parallel. You can choose between either of the two.

#### 9:00 – 10:30 **Prof. Immanuel Bloch**

*(MPQ & Ludwig-Maximilians-Universität, DE)*

##### Quantum Simulations using Ultracold Atoms in Optical Lattices

More than 30 years ago, Richard Feynman outlined his vision of a quantum simulator for carrying out complex calculations on physical problems. Today, his dream is a reality in laboratories around the world. In these lectures, I will give an introduction to quantum simulations using ultracold atoms trapped in optical lattices. We will cover basic cooling, trapping, manipulation and detection mechanisms for these systems including Quantum Gas Microscopes, which allow for single atom resolved detection with single lattice site resolution. In the second part of the lecture, I will outline a few applications regarding quantum simulations of condensed matter systems, namely the Fermi Hubbard model, which plays an essential role in the context of High-Tc superconductivity, experiments on new dynamical phases of matter, as well as topological systems.

#### 9:00 – 10:30 **Prof. Thomas Ebbesen**

*(ISIS, University of Strasbourg, FR)*

##### Manipulating Matter by Strong Coupling to the Vacuum Field

Over the past decade, there has been a surge of interest in the ability of hybrid light-matter states to control the properties of matter and chemical reactivity. Such hybrid states can be generated by simply placing a material in the spatially confined electromagnetic field of an optical resonator, such as that provided by two parallel mirrors. This occurs even in the dark because it is electromagnetic fluctuations of the cavity (the vacuum field) that strongly couple with the material. Experimental and theoretical studies have shown that the mere presence of these hybrid states can enhance properties such as transport, ferromagnetism, and superconductivity and modify (bio)chemical reactivity. This emerging field is highly multidisciplinary, and much of its potential has yet to be explored. In this lecture, this topic will be introduced together with some of the experimental and theoretical challenges.

For a review on the topic please see: Garcia-Vidal, Ciuti, Ebbesen, Science 373, eabd0336 (2021)

**10:30 – 11:00**

#### Coffee break

**11:00 – 12:30**

#### Student talks

**Location**: ISIS building, Esplanade campus

#### Lisa Sommer

*(University of Münster, IBM Research Zürich)*

**Cool Schottky Contacts**

Silicon fin field-effect transistors (FinFETs) are used in classical CMOS electronics but can also provide an attractive platform for the implementation of spin qubits [1,2]. Classical transistors usually have highly doped contacts that determine device polarity (n-type or p-type). Our FinFETs have Schottky contacts formed by a silicide. These contacts can be ambipolar [3] if a midgap silicide is used (NiSi). For a low contact resistance to holes, PtSi is more suitable because it has a lower Schottky barrier height. In my project the goal is to study the physics of these Schottky contacts and develop a low resistance n-type Schottky contact using e.g. ErSi. These contacts will then be used to operate electron spin qubit devices like the ones that have already been demonstrated with hole spins.

[1] R. Maurand et al. Nat Commun (2016)

[2] L. Camenzind et al. ArXiv (2021)

[3] A. Kuhlmann et al. APL (2018)

#### Thomas Allard

*(Université de Strasbourg)*

**Disorder-enhanced transport in a chain of lossy dipoles strongly coupled to cavity photons**

In one-dimensional systems with short range interaction, it is known from the theory of Anderson localization that an infinitesimal amount of disorder makes all the eigenstates of the system exponentially localized. However, for more complex interactions the effects of disorder become highly nontrivial.

Recently, it has been proposed [1,2] to use the light-matter interaction in order to modify the localization properties of a disordered system, surprisingly leading to an improvement of its transport characteristics. Here, we study the interplay between disorder and light-matter coupling by considering a disordered one-dimensional chain of lossy dipoles coupled to a multimode optical cavity through a microscopically-derived minimal coupling Hamiltonian. Such a system, hosting polaritonic (hybrid light-matter) excitations, may be realized experimentally in a wide range of artificial systems where the dominant coupling mechanism is of dipolar nature, from macroscopic microwave helical antennas to plasmonic and dielectric nanoparticles or ultracold atoms.

By analyzing both the eigenspectrum and the driven-dissipative transport properties of our model, we find that in the strong-coupling regime, increasing disorder leads uncoupled dark states to acquire a photonic part, allowing them to inherit polaritonic long-range transport characteristics. Crucially, we show that this disorder-enhanced transport mechanism is increasingly noticeable when the considered dipoles are lossy.

[1] T. Botzung, D. Hagenmüller, S. Schütz, J. Dubail, G. Pupillo, and J. Schachenmayer, Dark state semilocalization of quantum emitters in a cavity, Phys. Rev. B 102, 144202 (2020)

[2] N. C. Chavez, F. Mattiotti, J. A. Méndez-Bermudez, F. Borgonovi, and G. L. Celardo, Disorder-enhanced and disorder-independent transport with long-range hopping: Application to molecular chains in optical cavities, Phys. Rev. Lett. 126, 153201 (2021)

#### Evangelia Aspropotamiti

*(University of Geneva)*

**Implementation of a Self-testing Quantum Random Number Generator**

Self-testing quantum random number generators have a unique place in quantum technologies, since they allow for the monitoring of the source’s entropy in real time by measuring the input-output statistics. Our device uses a prepare-and-measure protocol where two states are prepared, a coherent state or the vacuum, and then a detector performs unambiguous state exclusion to discriminate between them. The protocol is semi-device independent, while the randomness is certified only with an assumption on the overlap of the two prepared states. The QRNG is also self-testing, meaning that we can monitor the correct function of the setup in real-time. This implementation is a prototype, implemented in a box using off-the-shelf commercial components. With our simple setup we achieved real-time extraction of truly random numbers with a rate of ~7 MHz.

#### Nathan Roubinowitz

*(ENS Paris-Saclay, Karlsruher Institut für Technologie)*

**Majorana fermions in interaction with sub- and supraluminal solitons in topological Josephson Junctions**

Majorana fermions in condensed matter systems are of great interest for their applications in quantum information processing. One can find them at the edges of two-dimensional time-reversal topological superconductors. Those edge states obey a Dirac equation with an effective speed of light. In a long Josephson junction made from such superconductors, the Dirac field is perturbed by solitons of the superconducting phase difference. One finds bound states localized on the soliton, and more particularly a zero-energy mode, also called Majorana bound state (MBS). By injecting external current, one can control those solitons and make them move slower or faster than the effective speed of light. We study the excitation of all edge states by the passage of a sub- and supraluminal soliton and calculate analytically the induced particle current and energy density. We deduce under which conditions the information encoded in the MBS can be read by a detector.

#### Elsie Loukiantchenko

*(TU Delft, European Space Agency)*

**Towards a Global Satellite Quantum Network: Optimized Key Rate Estimation in a Dynamic Satellite System**

Quantum networks will undoubtedly play crucial role in advancing quantum technologies including quantum communication, distributed quantum computing, and quantum metrology. Currently a nascent topic, the fundamental understanding of how to properly and efficiently simulate usable quantum networks will have a profound impact on how to design and implement this technology on a global scale. In one application, such networks are used in quantum communication, wherein provably-secure quantum encryption protocols face important challenges. Reaching high key transmission rates over long distances through fiber or atmosphere is difficult due to exponential photon loss, and can be ameliorated by incorporating satellite links into the quantum communication network. Within this project, an optimized theoretical framework for a global network of satellites will be developed.

The goal of this project is to develop a modular channel model which includes all relevant sources of noise and loss in such a system, and to create an optimization tool which selects the best parameters for a given infrastructure. This will also take into account satellite orbits and their effects on communication windows. Once a single link system has been established, we will be able to simulate a dynamic multi-satellite network with several ground stations, with room for further optimization for parameters such as the minimum number of satellites. Ultimately, we will provide a modular approach for simulating a global network for various cryptographic schemes and satellite constellations, paving the way for a global quantum internet.

**12:30 – 14:00**

#### Lunch

**Location**: CROUS Resto’U Paul Appel**Cost:** free

We will have lunch together at Crous.

**14:00 – 15:30**

#### In-depth lectures

**Location**: ISIS building, Esplanade campus.

Courses will be given in parallel. You can choose between either of the two.

#### 14:00 – 15:30 **Prof. Stéphane Berciaud**

*(IPCMS, University of Strasbourg, FR)*

##### Emergent quantum phenomena in van der Waals heterostructures

The quest for low-dimensional systems with novel quantum properties is one of the most active research efforts in materials science. In this context, two-dimensional (2D) materials (such as mono of few-layers of graphene, boron nitride, transition metal dichalcogenides or magnetic layered materials) compose a broad palette of atomically-thin crystals with remarkable electronic, optical, spin, valley and even mechanical properties. These assets can be enhanced *ad lib* by stacking 2D layers into so-called van der Waals heterostructures and thereby tailoring novel functionalities and devices that cannot be achieved using more conventional materials and low-dimensional heterostructures.

These two lectures aim at introducing 2D materials and some of their peculiar quantum properties. The first lecture will introduce the physics of some of the most popular 2D systems (namely graphene and atomically-thin semiconductors) and selection of landmark experiments, presented with a “historical” perspective. The second lecture will focus on van der Waals engineering, explaining how exquisite control of the stacking sequence, nanoscale environment and rotational mismatch (the so-called twist angle) have recently led to beautiful discoveries with outcomes for quantum photonics and (opto-)electronics.

Selected recent reviews:

A. H. Castro Neto *et al.*, “The electronic properties of graphene”, *Rev. Mod. Phys.* **81**, 109 (2009)

G. Wang *et al.*, “Colloquium: Excitons in atomically thin transition metal dichalcogenides”, *Rev. Mod. Phys. ***90**, 021001 (2018)

N. Wilson *et al.*, “Excitons and emergent quantum phenomena in stacked 2D semiconductors”, *Nature* **599**, 383 (2021)

#### 14:00 – 15:30 **Dr. Fabian Steinlechner **

*(Fraunhofer IOF, DE)*

##### Quantum Communication in space

**15:30 – 18:00**

#### Poster session 1

**Location**: ISIS building, Esplanade campus.

In the poster sessions you will have the opportunity to present your own research to other participants and exchange ideas and discuss results. Refreshments will also be served.

Your name badge shows your unique participant number. Participants **1 – 50** will present in the poster session 1, 51-100 in the second poster session on Wednesday.

**19:30 – 23:00**

#### Science Pub Quiz

**Location:** K’fet de chimie, Esplanade campus.**Fee:** free

*Why should you pet your basil plant from time to time? What is the IKEA effect? And does an onion float?*

Together with your team you will find answers to these and many more questions during the Science Pub Quiz. Not only will this trivia game expand your knowledge about everyday science questions but it will also be a fun way to make connections with other participants in a casual setting. Refreshments will be served.

image credits: Science Pub Quiz

#### Wednesday

**9:00-10:30**

#### Introductory lectures

**Location**: ISIS building, Esplanade campus

#### 9:00 – 9:45 **Prof. Anaï**s** Dréau**

*(L2C, CNRS & University of Montpellier, FR*)

##### Fluorescent spin-defects for quantum technologies

Optically-active spin defects in semiconductors are solid-state artificial atoms that can maintain their quantum properties over very long times, and sometimes up to room-temperature. A review of their appealing properties for quantum applications, such as ultra-sensitive nanoscale quantum sensors, multi-spin clusters for quantum information processing and quantum communication networks, will be presented. Current challenges towards large-scale implementation of quantum technologies and the exploration of novel platforms to isolate individual spin defects will be addressed.

#### 9:45 – 10:30 **Prof. Wolfgang Lechner**

*(Universität Innsbruck and CEO Parity QC, AT)*

##### Quantum Computing on Near Term Devices

The current worldwide interest in building fault tolerant quantum computers is motivated by the prospect of solving classical computational problems exponentially faster. However, there are still fundamental experimental challenges in building error corrected quantum computers and thus the goal is to make use of existing quantum computing and also quantum simulation devices for computation. I will introduce the current research directions for these near term devices and give an overview of gate model approaches, quantum simulation approaches, measurement based computing and adiabatic quantum computing. A focus will be the use of quantum simulation tools for computational tasks using adiabatic quantum computing.

**10:30 – 11:00**

#### Coffee break

**11:00 – 12:30**

#### Student talks

**Location**: ISIS building, Esplanade campus.

#### Lucas Leclerc

*(Université Paris-Saclay, Pasqal)*

**PUSHO, a pulse-level variational quantum algorithm for Rydberg atom platforms**

The manipulation of neutral atoms by light is at the heart of countless scientific discoveries in the field of quantum physics in the last three decades. The level of control that has been achieved at the single particle level within arrays of optical traps, while preserving the fundamental properties of quantum matter (coherence, entanglement, superposition), makes these technologies prime candidates to implement disruptive computation paradigms.

The current quantum processors (QPU) are nothing close to universal computers but can already target specific combinatorial problems whose classical complexity scales exponentially with their size, such as finding the Maximum Independent Set (MIS) of a Unit-Disk (UD) graph. Mapping those problems to Rydberg platforms enables to solve them by approximating their cost function with the Hamiltonian of the system. Then the atoms are optimally driven to a solution state which minimises the previous cost with pulses shaped by Bayesian optimisation. Pulse Shaping Optimisation (PUSHO) provides a straightforward but powerful Variational Quantum Algorithm (VQA), taking advantage of our ability to precisely control the shape of the driving fields.

#### Verena Feulner

*(Friedrich-Alexander-Universität Erlangen-Nürnberg)*

**Variational Quantum Eigensolver for the J1-J2-model**

The ground state properties of the two-dimensional J1-J2-model are very challenging to analyze via classical numerical methods, which makes the model a promising candidate where quantum computers could be helpful and possibly explore regimes that classical computers cannot reach.The J1-J2-model is a quantum spin model composed of Heisenberg interactions along the rectangular lattice edges and along diagonal edges between next-nearest neighbor spins.We propose an ansatz for the Variational Quantum Eigensolver (VQE) to approximate the ground state of an antiferromagnetic J1-J2-Hamiltonian for different lattice sizes and different ratios of J1 and J2. Moreover, we demonstrate that this ansatz can work without the need for gates along the diagonal next-nearest neighbor interactions. This simplification is of great importance for solid state based hardware with qubits on a rectangular grid, where it eliminates the need for SWAP gates.In addition, we give an outlook on the number of gates and parameters needed for larger lattice sizes.

#### Alexander Kliesch

*(Technical University Munich)*

**Twisted hybrid algorithms for combinatorial optimization**

We argue that for certain optimization problems, variational quantum algorithms such as the Quantum Approximate Optimization Algorithm can be further hybridized. Specifically, we consider combining a quantum variational ansatz with a greedy classical post-processing procedure for the MaxCut problem on 3-regular graphs. We show that the average cut-size can be quantified in terms of the energy of a modified problem Hamiltonian. This motivates the consideration of an improved algorithm which variationally optimizes the energy of that Hamiltonian. We call this a twisted hybrid algorithm and give analytic lower bounds on the expected approximation ratios achieved by twisted QAOA. These show that the necessary non-locality of the quantum ansatz can be reduced: For small levels, we show that compared to the original QAOA, the level can be reduced by one while roughly maintaining the expected approximation ratio.

#### Edward Deacon

*(University of Bristol)*

**An Introduction to Integrated Quantum Photonics for Quantum Computing**

Integrated quantum photonics (IQP) offers a promising platform for quantum computing: circuits are small, reconfigurable and scalable, with the manufacture of IQP chips supported by mature CMOS processes; photons suffer little from decoherence and travel fast enabling long-distance transmission of information along optical fibres; and photons are measured easily allowing fast readout of quantum states. IQP is not without challenges however, with notable examples being photon loss and the deterministic generation of photons. Here we present an introduction to IQP for quantum computing and highlight recent work towards developing the platform, namely creating near unity purity photon sources in silicon [1] and the implementation of reconfigurable graph states with four and eight qubits with the latter using an error protection protocol [2,3].

[1] Paesani, S., Borghi, M., Signorini, S. et al. Near-ideal spontaneous photon sources in silicon quantum photonics. Nat Commun 11, 2505 (2020).

[2] Adcock, J.C., Vigliar, C., Santagati, R. et al. Programmable four-photon graph states on a silicon chip. Nat Commun 10, 3528 (2019).

[3] Vigliar, C., Paesani, S., Ding, Y. et al. Error-protected qubits in a silicon photonic chip. Nat. Phys. 17, 1137–1143 (2021).

#### Camille Le Calonnec

*(Université de Strasbourg)*

**Floquet theory for a fast and high fidelity parametric-two-qubit gates**

A major challenge in realizing scalable quantum computers is the optimization of two-qubit entangling gates. The realization of high-fidelity quantum gates involves a multitude of parameters governing important properties of the system, such as the gate rate, leakage, spurious interactions etc. One therefore needs to carefully choose these parameters to optimize the gate speed while minimizing unwanted cross-Kerr interaction. Numerically, this can be a resource intensive process as it implies simulating the gate dynamics for each set of device parameters. We present a method based on Floquet theory to extract the interaction rates without having to run full dynamical simulations. We apply this technique to a new two-qubit entangling parametric gate developed in collaboration with Princeton. First experimental results show the realisation of a sqrt(iSWAP) gate in 13 ns with 99.8% fidelity, which is one of the best in the field.

**12:30 – 14:00**

#### Lunch

**Location**: CROUS Resto’U Paul Appel**Cost:** free

We will have lunch together at Crous.

**14:00 – 15:30**

#### Introductory lectures

**Location**: ISIS building, Esplanade campus

#### 14:00 – 14:45 **Dr. Matthias Mergenthaler**

*(IBM Research, CH)*

##### Quantum Computing – From transistors to qubits and back

Over the past decade, platforms for implementing quantum computing architectures have seen rapid advances in technological development and understanding of their fundamental physical principles, bringing the promise of a quantum computer slightly closer to reality. Nevertheless, to make use of the potentially advanced computing capabilities of a quantum computer, the technology platforms need to be scaled from 10s of qubits today to >1000s of qubits. This will require significant effort in understanding the current limitations of the different platforms.

In the first lecture I will give an introduction to quantum computing and its underlying principles. Further, I will give an overview of the technology, the applications and the tools IBM is developing in the space of quantum computing.

#### 14:45 – 15:30 **Prof. Anja Metelmann**

*(Karlsruhe Institute of Technology and University of Strasbourg, DE/FR)*

##### The Realm of Engineered Quantum Systems

The introductory lecture focuses on the fundamental aspects and applications of engineered quantum systems for quantum information science and technologies. Within these systems one aims to harness the power of quantum for novel quantum technologies and optimized protocols in quantum information processing, sensing and communication. I will give a brief overview on superconducting and electro-mechanical platforms and discuss some of their future applications.

**15:30 – 18:00**

#### Poster session 2

**Location**: ISIS building, Esplanade campus.

In the poster sessions you will have the opportunity to present your own research to other participants and exchange ideas and discuss results. Refreshments will also be served.

Your badge shows your unique participant number. Participants **51 – 100** will present in the poster session 2.

**19:30 – 22:00**

#### Conference dinner

**Location:** Au Brasseur**Cost:** free

For the last evening of the spring school we invite you to a typical Alsatian restaurant and enjoy local food and beverages in a relaxed atmosphere.

#### Thursday

**9:00-10:30**

#### In-depth lectures

**Location**: ISIS building, Esplanade campus.

Courses will be given in parallel. You can choose between either of the two.

#### 9:00 – 10:30 **Prof. Anaï**s** Dréau**

*(L2C, CNRS & University of Montpellier, FR)*

##### The NV center in diamond: a versatile qubit for quantum technologies

The nitrogen-vacancy (NV) center in diamond is by far the most advanced fluorescent spin defect for quantum technologies. Its remarkable spin properties enable to use it as a robust and versatile qubit to develop a large range of quantum applications including nanoscale quantum sensors, multi-spin quantum processors and quantum networks.

In this second lecture, we will explore the physics of this fantastic quantum system. We will learn how to create this fluorescent spin defect and control its quantum properties. At last, we will discuss its interactions with the environment, the resulting limitations on its spin coherence time and how to get rid of them.

#### 9:00 – 10:30 **Prof. Wolfgang Lechner**

*(Universität Innsbruck and CEO Parity QC, AT)*

##### Quantum Computing on near term devices

The current worldwide interest in building fault tolerant quantum computers is motivated by the prospect of solving classical computational problems exponentially faster. However, there are still fundamental experimental challenges in building error corrected quantum computers and thus the goal is to make use of existing quantum computing and also quantum simulation devices for computation. I will introduce the current research directions for these near term devices and give an overview of gate model approaches, quantum simulation approaches, measurement based computing and adiabatic quantum computing. A focus will be the use of quantum simulation tools for computational tasks using adiabatic quantum computing.

**10:30 – 10:45**

#### Coffee break

**10:45 – 12:15**

#### In-depth lectures

**Location**: ISIS building, Esplanade campus.

Courses will be given in parallel. You can choose between either of the two.

#### 10:45 – 12:15 **Prof. Anja Metelmann**

(*Karlsruhe Institute of Technology and University of Strasbourg, DE/FR)*

##### Interplay of coherent and dissipative processes in engineered quantum systems

The in-depth lecture focuses on the engineering and control of coherent and dissipation parametric processes in engineered quantum systems. One crucial aspect is here that dissipation, which in general limits the performance of an experiment, is turned into an advantageous tool. Such concepts of dissipation engineering have enriched the methods available for state preparation, dissipative quantum computing and quantum information processing. Combining such engineered dissipative processes with coherent dynamics allows for new effects to emerge. For example, we found that any factorisable (coherent) Hamiltonian interaction can be rendered nonreciprocal if balanced with the corresponding dissipative interaction. This powerful concept can be exploited to engineer nonreciprocal devices for quantum information processing, computation and communication protocols, e.g., to achieve control over the direction of propagation of photonic signals. In this talk I will introduce the basic concept and discuss possible experimental implementations.

#### 10:45 – 12:15 **Dr. Matthias Mergenthaler**

*(IBM Research, CH)*

##### Quantum Computing – From transistors to qubits and back

Over the past decade, platforms for implementing quantum computing architectures have seen rapid advances in technological development and understanding of their fundamental physical principles, bringing the promise of a quantum computer slightly closer to reality. Nevertheless, to make use of the potentially advanced computing capabilities of a quantum computer, the technology platforms need to be scaled from 10s of qubits today to >1000s of qubits. This will require significant effort in understanding the current limitations of the different platforms.

In the second lecture I will cover two different topics. At first, I will explain why understanding the materials from which the qubits are made is critical for further developments in improving qubit quality, using research with superconducting qubits. Secondly, I will introduce another qubit technology, namely spin qubits in silicon, and how they may help in scaling to larger quantum systems.

**12:15 – 13:15**

#### Lunch

**Location**: CROUS Resto’U Paul Appel**Cost:** free

We will have lunch together at Crous.

**14:00 – 18:00**

#### Lab tours and industry fair

**Location**: IPCMS, Cronembourg

#### 14:00 – 18:00 **Lab tours**

Motivated local students will show you around their labs at IPCMS and ISIS.

#### 14:00 – 18:00 Industry fair** **

At the central meeting point you will have the chance to exchange with representatives from the quantum industry, allowing you to explore career opportunities beyond academia and find out more about the latest quantum tech.

The following companies will be at display: