Environment-assisted quantum transport in a 10-qubit network

The way in which energy is transported through an interacting system governs fundamental properties in many areas of physics, chemistry, and biology. Remarkably, environmental noise can enhance the transport, an effect known as environment-assisted quantum transport (ENAQT). In this paper, we study ENAQT in a network of coupled spins subject to engineered static disorder and temporally varying dephasing noise. The interacting spin network is realized in a chain of trapped atomic ions and energy transport is represented by the transfer of electronic excitation between ions. With increasing noise strength, we observe a crossover from coherent dynamics and Anderson localization to ENAQT and finally a suppression of transport due to the quantum Zeno effect. We found that in the regime where ENAQT is most effective the transport is mainly diffusive, displaying coherences only at very short times. Further, we show that dephasing characterized by non-Markovian noise can maintain coherences longer than white noise dephasing, with a strong influence of the spectral structure on the transport effciency. Our approach represents a controlled and scalable way to investigate quantum transport in many-body networks under static disorder and dynamic noise.Comment: Mai

Observation of Entangled States of a Fully Controlled 20-Qubit System

We generate and characterise entangled states of a register of 20 individually controlled qubits, where each qubit is encoded into the electronic state of a trapped atomic ion. Entanglement is generated amongst the qubits during the out-of-equilibrium dynamics of an Ising-type Hamiltonian, engineered via laser fields. Since the qubit-qubit interactions decay with distance, entanglement is generated at early times predominantly between neighbouring groups of qubits. We characterise entanglement between these groups by designing and applying witnesses for genuine multipartite entanglement. Our results show that, during the dynamical evolution, all neighbouring qubit pairs, triplets, most quadruplets, and some quintuplets simultaneously develop genuine multipartite entanglement. Witnessing genuine multipartite entanglement in larger groups of qubits in our system remains an open challenge.Comment: 20 pages, 4 figure

Predicting molecular vibronic spectra using time-domain analog quantum simulation

Spectroscopy is one of the most accurate probes of the molecular world. However, predicting molecular spectra accurately is computationally difficult because of the presence of entanglement between electronic and nuclear degrees of freedom. Although quantum computers promise to reduce this computational cost, existing quantum approaches rely on combining signals from individual eigenstates, an approach that is difficult to scale because the number of eigenstates grows exponentially with molecule size. Here, we introduce a method for scalable analog quantum simulation of molecular spectroscopy, by performing simulations in the time domain. Our approach can treat more complicated molecular models than previous ones, requires fewer approximations, and can be extended to open quantum systems with minimal overhead. We present a direct mapping of the underlying problem of time-domain simulation of molecular spectra to the degrees of freedom and control fields available in a trapped-ion quantum simulator. We experimentally demonstrate our algorithm on a trapped-ion device, exploiting both intrinsic electronic and motional degrees of freedom, showing excellent quantitative agreement for a single-mode vibronic photoelectron spectrum of SO$_2$.Comment: 13 pages, 8 figure

International Conference on Quantum Technologies for High-Energy Physics (QT4HEP22)

Trapped ions are one of the leading and furthest developed technologies in quantum computing. However, despite higher quality operations than on any other platform and the absence of variations in qubit quality, the road to fault-tolerant quantum computing remains long and steep. In this talk, I will briefly review the state of the art of the trapped-ion platform, illustrate the current attempts to scaling up to larger numbers of qubits and highlight the challenges faced in control electronics and reliable manufacturing

Digital quantum simulation, Schrödinger cat state spectroscopy and setting up a linear ion trap

In dieser Dissertationsschrift wird über zwei Experimente auf dem Gebiet der Quanteninformationsverarbeitung mit gespeicherten Kalzium-Ionen berichtet. Zusätzlich werden der Aufbau und die Charakterisierung einer neuen linearen Paul-Falle sowie die Implementierung einer neuartigen akustooptischen Adressierung einzelner Ionen vorgestellt. Das erste der beiden Experimente beschäftigt sich mit dem Machbarkeitsnachweis von digitalen Quantensimulationen unter Verwendung von bis zu 6 Ionen und 100 Gatteroperationen. Es untersucht die Skalierbarkeit von Simulationen elementarer Modelle des Magnetismus im Hinblick auf die Anzahl der beteiligten Spins und die Komplexität ihrer gegenseitigen Wechselwirkungen. Das zweite Experiment stellt die Anwendung eines Schrödinger-Katzen-Zustands zum indirekten Nachweis von Einzelphotonen-Streuvorgängen an einem breiten elektronischen Übergang vor. In einer Machbarkeitsstudie mit einem Ionenkristall unterschiedlicher Isotope aus 40Ca+ und 44Ca+ wird die Empfindlichkeit der Methode bis hin zum Niveau einzelner Photonen demonstriert. Die Arbeit schließt mit einem kurzen Ausblick auf zukünftige Untersuchungen und Erweiterungen des experimentellen Aufbaus.This PhD thesis reports on two experiments in the field of quantum information processing using trapped calcium ions. In addition, the text covers the setup and characterization of a new linear Paul trap accompanied by a novel implementation of single-ion addressing using an acousto-optic deflector. The first of the two experiments is concerned with the proof-of-principle implementation of digital quantum simulations using up to 6 ions and 100 gate operations. It investigates the scaling behavior of simulations of elementary models of magnetism in terms of the number of involved spins and the complexity of their mutual interactions. The second experiment introduces the application of a Schroedinger cat state in the indirect detection of photon scattering events on a broad electronic transition. The method is shown to have a sensitivity down to the single photon level in a proof-of-principle demonstration using a mixed-isotope crystal of 40Ca+ and 44Ca+. A brief outlook towards future experiments and extensions of the experimental setup concludes the manuscript.by Cornelius HempelAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersEnth. u.a. 2 Veröff. d. Verf. aus den Jahren 2011 - 2013 . - Zsfassung in dt. SpracheInnsbruck, Univ., Diss., 2014OeBB(VLID)19795