Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - AQSuS (Analog Quantum Simulation using Superconducting Qubits)

Teaser

The remarkable progress in experimental physics over the last decade has enabled us to manipulate, control and detect the state of various quantum systems to a very high degree. Initially the interest in these kind of systems came from quantum information processing...

Summary

The remarkable progress in experimental physics over the last decade has enabled us to manipulate, control and detect the state of various quantum systems to a very high degree. Initially the interest in these kind of systems came from quantum information processing applications (QIP) - the goal to build a quantum computer - and the desire to understand more fundamentally the interactions in many-body systems. The realization of a universal quantum computer though has proven to be a very demanding goal. As a consequence the focus has shifted to simulating specific quantum phenomena. The unifying idea is to build a well-controlled device that mimics a certain quantum system that is either very hard to or cannot be simulated with a classical computer.

One of the most studied systems in this context are interacting spins. These spin systems serve as simple models for various quantum phenomena. There has been a steady progress simulating the physics of one-dimensional spin chains on various platforms and even first attempts on observing spin physics on two-dimensional lattices. So far though it still poses an open experimental challenge to realize a system with the necessary control to study spin dynamics in two dimensions.
In this ERC project we are implement an experimental platform for an analog quantum simulator of interacting spin systems using superconducting qubits. The scheme builds on the remarkable recent developments in circuit quantum electro dynamics systems. We will make use of the sophisticated control and readout schemes available in this platform to build interacting spins systems in one and two dimensions. As superconducting qubits are built with micro and nanofabrication processes this approach is in principle scalable. Combining these advantages would open up a range of new directions. Especially, it will allow us to investigate quantum phenomena in one and two dimensions where even existing numerical and analytical approaches reach their limitations. The impact of our expected results will range from condensed matter to quantum optics, quantum information and solid state physics.

In the past 18 month we have installed and tested the experimental setup i.e. the cryostat and the microwave equipment. Furthermore we have implemented all fundamental building blocks, superconducting resonators, qubits and waveguides which are necessary to build up the quantum simulation platform.

Work performed

The work that has been performed from the start of the project to the end of the 18 month period followed closely the proposed time plan and tasks in the project. This can be seen by the checked boxes in Table 1 and the summary after:

Image attached_Table 1
Table 1: Overview of the project work and time plan. The color code used for the different blocks is: Blue refers to design and cleanroom fabrication steps which will have to be repeated several times during the course of the project. Green refers to technology development and hardware setup necessary to reach the project goals. Orange to intermediate results and publishable goals. Red to high profile publications and core objectives of the project. The boxes which have check marks in them have been already done. The x marks a task which has been skipped as better results are expected upon a direct implementation in the wQED setup.


Work Summary

Month 1- 6:
• Work on the project began immediately with two PhD Students, two Master Students and one PostDoc which was paid out of a different fund for the first 12 month.
• The cryostat was installed and tested in the first month of the project. Within the next month we installed cryo-compatible microwave control and readout lines as well as low noise amplifiers and filters. The room temperature microwave setup and experimental control was established by the end of month 6.
• Finite element simulation was used to determine the parameters of the 3D cavity, the waveguide and the stripline resonator. The waveguide and the 3D cavity were manufactured in our workshop. The qubits were fabricated in the cleanrooms of the Karlsruhe Institute of Technology cleanroom and the stripline resonators were fabricated by the Research Centre for Microtechnology at the Vorarlberg University of Applied Sciences in Dornbirn, Austria. The external fabrication was necessary as the cleanroom facilities in Innsbruck where not yet ready to be used.
• We experimentally evaluated the design and determined the quality factors of the stripline resonators inside the waveguide setup. These results were published in AIP Advances 7, 085118 (2017).
Month 7-12

• Within the first year we realized a key experimental goal, a two qubit cQED setup to characterize the interaction between the qubits. Furthermore we realized a novel way for fast flux control of superconducting qubits within a 3D waveguide cavity. We characterized the spin-spin interaction, measured coherence times (T1 & T2 > 20µs) and residual thermal population (pe < 4%) in the setup. These are important factors for the future development of the project.
• We implemented a quantum limited amplifier into our setup to make use of the increased signal-to-noise ratio and single shot readout capabilities. We realized detection fidelities of more than 98% within a detection time of 400ns. We are currently working on extending these capabilities to a multi qubit readout.
• In May 2018 our own cleanroom facilities became available and we have been working on implementing the recipes to fabricate superconducting Transmon qubits and waveguide resonators.
• We implemented the wQED architecture and could already verify spin-spin interaction mediated via photons within this waveguide.

Month 13 - 18

• We carefully evaluated our fast flux tuning technology and its impact on qubit coherence time and population. These findings have been written up and recently been submitted to PRL, a preprint version can be found on arxiv.XXXX
• We have implemented two different interacting four qubit system within our wQED setup. In one instance we have realized a four qubit lattice with equal all to all coupling, constituting a small 2D lattice. The second system constitutes of two pairs of qubits which are coupled via a photon mediated interaction through the waveguide. Each pair consists of two capacitive coupled qubits. These two systems are two corner stones for the work within the project on open sys

Final results

In summary the main innovations are:
• Natural implementation of strongly interacting 2D spin models with arbitrary lattice geometries.
• Investigate currently inaccessible quantum phenomena in 2D systems.
• Combine open system dynamics with strongly interacting spin systems which opens up a new approach to investigate interacting quantum many body problems.
• Provide valuable insight into strongly interacting superconducting qubit systems which will affect design considerations in cQED quantum information processing and quantum simulation applications.
The impact of the expected results of this project will range from condensed matter to quantum optics, quantum information and solid state physics and will allow the investigation of quantum many body problems which are inaccessible with current technology.

Website & more info

More info: https://iqoqi.at/en/research-gk/projects/609-analog-quantum-simulation-using-superconducting-qubits.