Observation of quantum domain melting and its simulation with a quantum computer

Domains are homogeneous areas of discrete symmetry, created in nonequilibrium phase transitions. They are separated by domain walls, topological objects which prevent them from fusing together. Domains may reconfigure by thermally-driven microscopic processes, and in quantum systems, by macroscopic quantum tunnelling. The underlying microscopic physics that defines the system's energy landscape for tunnelling is of interest in many different systems, from cosmology and other quantum domain systems, and more generally to nuclear physics, matter waves, magnetism, and biology. A unique opportunity to investigate the dynamics of microscopic correlations leading to emergent behaviour, such as quantum domain dynamics is offered by quantum materials. Here, as a direct realization of Feynman's idea of using a quantum computer to simulate a quantum system, we report an investigation of quantum electron reconfiguration dynamics and domain melting in two matching embodiments: a prototypical two-dimensionally electronically ordered solid-state quantum material and a simulation on a latest-generation quantum simulator. We use scanning tunnelling microscopy to measure the time-evolution of electronic domain reconfiguration dynamics and compare this with the time evolution of domains in an ensemble of entangled correlated electrons in simulated quantum domain melting. The domain reconfiguration is found to proceed by tunnelling in an emergent, self-configuring energy landscape, with characteristic step-like time evolution and temperature-dependences observed macroscopically. The remarkable correspondence in the dynamics of a quantum material and a quantum simulation opens the way to an understanding of emergent behaviour in diverse interacting many-body quantum systems at the microscopic level.Comment: 11 pages, 2 figure

Quantum billiards with correlated electrons confined in triangular transition metal dichalcogenide monolayer nanostructures created by laser quench

Forcing systems though fast non-equilibrium phase transitions offers the opportunity to study new states of quantum matter that self-assemble in their wake. Here we study the quantum interference effects of correlated electrons confined in monolayer quantum nanostructures, created by femtosecond laser-induced quench through a first-order polytype structural transition in a layered transition-metal dichalcogenide material. Scanning tunnelling microscopy of the electrons confined within equilateral triangles, whose dimensions are a few crystal unit cells on the side, reveals that the trajectories are strongly modified from free-electron states both by electronic correlations and confinement. Comparison of experiments with theoretical predictions of strongly correlated electron behaviour reveals that the confining geometry destabilizes the Wigner/Mott crystal ground state, resulting in mixed itinerant and correlation-localized states intertwined on a length scale of 1 nm. Occasionally, itinerant-electron states appear to follow quantum interferences which are suggestive of classical trajectories (quantum scars). The work opens the path toward understanding the quantum transport of electrons confined in atomic-scale monolayer structures based on correlated-electron-materials

Introduction to quantum computing

I will give an overview of the quantum computing landscape, existing quantum hardware, quantum algorithms, quantum error correction, and the quantum internet

Konfiguracijska elektronska stanja v plastovitih prehodno kovinskih dihalkogenidih

Mesoscopic irregularly ordered and even amorphous self-assembled electronic structures were recently reported in two-dimensional metallic dichalcogenides (TMDs), created and manipulated with short light pulses or by charge injection. Apart from promising new all-electronic memory devices, such states are of great fundamental importance, since such aperiodic states cannot be described in terms of conventional charge-density-wave (CDW) physics. In this thesis, we first address the problem of metastable mesoscopic configurational charge ordering in TMDs with a sparsely filled charged lattice gas model in which electrons are subject only to screened Coulomb repulsion. The model correctly predicts commensurate CDW states corresponding to different TMDs at magic filling fractions $f_m=1/3,1/4,1/9,1/13,1/16$. Doping away from $f_m$ results either in multiple near degenerate configurational states, or an amorphous state at the correct density observed by scanning tunneling microscopy. Quantum fluctuations between degenerate states predict a quantum charge liquid at low temperatures, revealing a new generalized viewpoint on both regular, irregular and amorphous charge ordering in transition metal dichalcogenides. During the development of our model we also found it useful in three other examples of experiments. The first application of the model deals with theoretical modeling of the non-equilibrium amorphous state in 1T-TaS$_2$. The second application deals with quantum billiards of correlated electrons confined in triangular transition metal dichalcogenide monolayer nanostructures created by laser quench. The third and last application of our model deals with a time-domain phase diagram of metastable states in a charge ordered quantum material. Finally, we extend our classical version of the model to the quantum regime and deploy it on D-Wave’s quantum computer. We explore the observation of quantum domain melting and its simulation with a quantum computer.Nedavne raziskave poročajo o mezoskopskih nepravilno urejenih in celo amorfnih samosestavljenih elektronskih strukturah v dvodimenzionalnih prehodno kovinskih dikalkogenidih (PKD), ustvarjenih in manipuliranih s kratkimi svetlobnimi impulzi ali z injekcijo naboja. Poleg tega, da obetajo nove vseelektronske pomnilniške naprave, so takšna stanja zelo pomembna, saj takšnih aperiodičnih stanj ni mogoče opisati s konvencionalno fiziko valov gostote naboja (VGN). V tej disertaciji najprej obravnavamo problem metastabilnega mezoskopskega konfiguracijskega urejanja naboja v PKD z modelom redkega nabitega plina na rešetki, v katerem med elektroni obstaja le senčen Coulombov odboj. Model pravilno napoveduje komenzurabilna stanja VGN, ki ustrezajo različnim PKD pri magičnih polnilih $f_m=1/3,1/4,1/9,1/13,1/16$. Dopiranje stran od $f_m$ povzroči bodisi več skoraj degeneriranih konfiguracijskih stanj, bodisi amorfno stanje pri določenem polnilu, ki ga opazimo z vrstično tunelsko mikroskopijo. Kvantne fluktuacije med degeneriranimi stanji napovedujejo kvantno tekočino nabojev pri nizkih temperaturah, kar razkriva nov posplošen pogled na urejeno, neurejeno in amorfno ureditev naboja v prehodno kovinskih dikalkogenidih. Med razvojem našega modela za razumevanje univerzalnih komenzurabilnih struktur VGN v PKD smo ugotovili, da je uporaben tudi pri drugih nepredvidenih aplikacijah v primeru različnih eksperimentov. V tej disertaciji predstavljamo tri tovrstne primere. Prva uporaba modela se nanaša na teoretično modeliranje neravnovesnega amorfnega stanja v 1T-TaS$_2$. Druga uporaba našega modela se nanaša na kvantni biljard koreliranih elektronov, ki so omejeni v trikotnih enoslojnih nanostrukturah prehodno kovinskega dikalkogenida, ustvarjenih z laserskimi sunki. Tretja in zadnja aplikacija našega modela se ukvarja s faznim diagramom metastabilnih stanj v kvantnem materialu z urejenim nabojem v časovni domeni. Nazadnje smo našo klasično različico modela razširili na kvantni režim in jo uporabili na kvantnem računalniku D-Wave. Raziskali smo opazovanje taljenja kvantnih domen in njegovo simulacijo s kvantnim računalnikom