Classical computers are made from semiconductors, but semiconductor-based architectures for quantum computers are still less developed than those based on superconducting circuits, trapped ions, or neutral atoms. I will try to convince you that there are good reasons to still pursue the "semiconductor path" to quantum computers, and discuss challenges that need to be overcome on this path. I will also discuss what kinds of interesting physical problems from solid state physics and open quantum system physics one can grapple with, while contributing to a somewhat "engineering-like" task of building a scalable quantum computer.

Proximity effects constitute a highly promising tool for versatile engineering of the band structure of graphene in van der Waals heterostructures [1]. Particularly promising relevant systems are based on transition metal dichalcogenides [2]. In the paper some approaches to tune the proximity effects in reversible manner will be discussed. A main one is based on charge density wave degree of freedom. Such a low-temperature ordering is known to develop in 1T polytypes of TaS₂ and NbS₂, enabling to manipulate the band structure of heterostructures in twistronic-like way without physical alteration of the twist angle.
In the paper the DFT calculations-based predictions of proximity effects in graphene band structure emerging in heterostructures with TaS₂ [3] and NbS₂ and controllable with charge density wave ordering will be presented. Moreover, magnetism in TaS₂ [4] will be discussed as yet another mechanism capable of shaping the proximity effects. Also the external electric field will be demonstrated to be an additional useful factor influencing the band structure.
The interpretation of the results will be based on symmetry-based tight-binding Hamiltonians [3]. Special emphasis will be put on proximity-induced Rashba spin-orbit coupling parametrized by characteristic energy and tuneable angle (inducing possible anisotropic Rashba–Edelstein effect).

Acknowledgements: Financial support provided by the University of Łódź under Grant No. 1/IDUB/DOS/2021 is gratefully acknowledged. Polish high-performance computing infrastructure PLGrid (HPC Centers: ACK Cyfronet AGH) is gratefully acknowledged for providing computer facilities and support within computational grant no. PLG/2023/016571.

[1] J. F. Sierra, J. Fabian, R. K. Kawakami, S. Roche and S. O. Valenzuela, Nature Nanotechnology 16 (2021) 856.
[2] M. Gmitra and J. Fabian, Physical Review B 92 (2015) 155403.
[3] K. Szałowski, M. Milivojević, D. Kochan and M. Gmitra, 2D Materials 10 (2023) 025013.
[4] I. Lutsyk, K. Szałowski et al., Nano Research 16 (2023) 11528.

The function of most proteins is strictly connected to their structure, which depends on their sequence and external factors, such as the surrounding environment. Interactions of proteins with lipid bilayers, for example, can significantly affect both systems and strongly depend on the lipid composition. This presentation will focus on demonstrating how external factors can impact protein structure and dynamics, examined through molecular dynamics simulations. I will present examples of several protein systems in bulk water, as well as when interacting or embedded into lipid bilayers of various compositions and how environmental conditions and other factors, such as the presence or absence of disulfide bonds, can influence them.

Critical metrology relies on the extreme sensitivity of the system's eigenstates close to the critical point to Hamiltonian parameter perturbations. Typically, however, the critical point, at which the phase transition occurs, is a function of many if not all the parameters of the system. This suggests that the quantum Fisher information matrix might be singular at the critical point, which in the context of parameter estimation is typically representing a significant complication. On the example of a toy-model Landau-Zener Hamiltonian, the Ising Hamiltonian, and the thermodynamic limit of the Lipkin-Meshkov-Glick Hamiltonian, we show that the quantum Fisher information matrix in critical metrology is always singular regardless of the system size and the distance to the critical point. However, contrary to the regular approach to metrology, where the singularity is detrimental, we argue that critical metrology works precisely because the quantum Fisher information matrix is singular.

Stalagmites are column-like formations that rise from the floor of caves. They are formed by the buildup of minerals deposited from water dripping from the ceiling. The water dissolves minerals, such as calcium carbonate, from the rock above. As the water drips down, it loses carbon dioxide to the cave air. This causes the minerals to come out of solution and precipitate onto the cave floor, slowly building up the stalagmite.

Nearly sixty years ago, Franke formulated a mathematical model for the growth of stalagmites. In this model, the local growth rate of a stalagmite is proportional to the oversaturation of calcium ions in the solution dripping down the stalagmite's surface. Franke postulated that - provided the physical conditions in the cave remain constant - after a sufficiently long period, the stalagmite will assume an ideal shape, which in later stages of growth will only move upwards without further change in its form. These conclusions were later confirmed in computer simulations yet the mathematical form of this ideal shape was not discovered.

As we will show, Franke's model for stalagmite growth can be solved analytically, finding invariant, Platonic forms of stalagmites that could be observed in an "ideal cave", under constant physical conditions and with a constant flow of water dripping from an associated stalactite. Interestingly, it turns out that the shape numerically found in previous numerical studies is just one of a whole family of solutions. These new solutions describe stalagmites with a flat area at their peak of a certain fixed diameter, and conical stalagmites, with sharply pointed tops. All of these forms are observed in caves.

Recent years have seen a surge of advancements in optical manipulation over bosonic light-matter quasiparticles known as exciton-polaritons in semiconductor microcavities. These particles appear under strong-coupling conditions between confined cavity photons and embedded quantum-well excitons. Characterised by very high interaction strengths, nonlinearities, and picosecond timescales, they provide an exciting testbed to explore room-temperature nonequilibrium Bose-Einstein condensation in the optical regime.

In this talk, I will present results on all-optically engineered macroscopic networks of connected exciton-polariton condensates, which permit studies on fundamental emergent behaviours in nonequilibrium quantum fluidic systems that are subject to an external drive and dissipation. I will explain how pumped polariton fluids give rise to so-called “ballistic condensates” which can interfere to form a bosonic analog of time-delay coupled oscillations, a behavior found all across nature. I will present experimental and theoretical results on large-scale condensate networks displaying aforementioned emergent behaviors, including: spontaneous synchronization with unprecedented long-range spatial and temporal correlations [1,2], formation of persistent circulating mass currents [3], non-invasive optical control of the network coupling weights [4], synthesis of artificial lattices for studies of non-Hermitian topological physics and Bloch band formation [5,6], and vortex frustration [7].

Lastly, I will discuss recent developments on the role of polariton condensate networks as nonlinear information processing elements in the optical computing paradigm. I will address three examples: room-temperature optical logic, analog spin simulators, and as neuromorphic computing hardware.

[1] Töpfer et al., Communication Physics 3, 2 (2020).
[2] Töpfer et al., Optica 8, 106 (2021).
[3] Cookson et al., Nature Communications 12, 2120 (2021).
[4] Alyatkin et al., Physical Review Letters 124, 207402 (2020).
[5] Pickup et al., Nature Communications 11, 4431 (2020).
[6] Alyatkin et al., Nature Communications 12, 5571 (2021).
[7] Alyatkin et al., arXiv:2207.01850 (2022).

Autonomy is a unique defining feature of living systems, from bacteria -- or even from viruses, the organisms at the 'edge of life' -- striving to survive in evolving environment. Yet, evolution is a collective phenomenon requiring interaction, 'counterintuitively' to autonomic thinking of individual organisms allowing their species to survive.
Such an apparent dichotomy and the struggle of the 'opposites' is ubiquitous in most complex dynamical systems, entailing complex adaptive systems which encompass living systems. The struggle of the opposites underlies most if not all roads to progress, understood as the evolution of 'fitness' -- be it adaptation to environment for species survival or evolution of scientific paradigms, or indeed, the evolution of the market share for those financially challenged.

Curiously, the concept of the 'roads to progress' has to date not sufficiently been studied using the language of physics of complexity. Indeed, physics traditionally understood, stayed away from investigating phenomena involving engaging in any laws of -- and due to -- individual and individualised behaviour. Yet, as becomes apparent, such seemingly impenetrable problems as evolution of social standards such as morality or religion are not principally different from evolution of scientific paradigms and innovation, these in turn not being that different from the evolution of generic actors in a competitive company market.

Such universality is where physics can flourish and indeed, a rapidly growing range of reports shows intriguing beauty of the phenomena characterising the dynamics of the road to progress. In my talk, I will present our own recent work on the game-of-life like system which - to our surprise - showed exciting richness of critical phenomena. I will also refer to selected works in order to encourage listeners to engage in research of the 'physics of struggle'.

A physical system may become non-conservative when it is interacting with its environment. One way to introduce openness is by breaking the Hermiticity, that is, by involving non-Hermitian matrices/operators. This seminar will provide a quick overview of the theoretical background of non-Hermitian physics, followed by a focus on the topic of non-Hermitian phase transitions intertwined with the physics of light-matter interactions.

In the initial part of the talk an extended overview will be presented on individual and collective spins, the states of the collective spin, squeezing the collective spin states. We will also talk about different spin squeezing mechanisms including one axis twisting (OAT), and two axis countertwisting (TACT) spin squeezing models. Subsequently we will discuss possibilities to produce spin squeezing for spinful atomic fermions in optical lattices. It is shown that by applying laser radiation one can simulate not only OAT but also TACT spin squeezing models, the latter TACT model providing better squeezing. The spin squeezing generated in this way is mediated by spin waves playing a role of the intermediate states facilitating the squeezing process. The spin squeezing can be used for increasing sensitivity of atomic clocks.

More about this work:
Phys. Rev. Lett. 129, 090403 (2022)
Phys. Rev. B 108, 104301 (2023)