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Noise-Enhanced Quantum Control

Periodic Reporting for period 1 - NEQC (Noise-Enhanced Quantum Control)

Reporting period: 2018-04-01 to 2020-03-31

Operating state-of-the-art quantum circuits is typically limited by noise, especially if they work in the microwave domain like superconducting quantum bits, qubits. Instead of trying to avoid noise, this project enables a circuit architecture that profits from it. The concept of transforming noise from an omnipresent obstacle into a useful resource in quantum control experiments will renew the field of circuit quantum electrodynamics (QED). The project implements noise-enhanced quantum control by integrating photon-assisted single-electron tunneling (SET) devices into superconducting qubits. This integration allows for quantum control because we can measure the qubit state and in return manipulate the qubit dynamics and its degrees of freedom. Such quantum control experiments that utilize noise will impact research in quantum computing, nano-electronics, and quantum simulations of chemical compounds. Hence, my proposed circuit realization will expand the range of possible applications of state-of-the-art quantum circuits. Furthermore, qubits with tunable decoherence rates will extend the current knowledge of dynamics in dissipative open quantum systems.

The project outcomes help in future applications beyond basic science. The expected societal impact of the project is based on the fact that quantum effects in superconducting nano-electronics occur in both large-scale quantum computers and in novel sensing applications. Both topics belong to long-term scientific goals and can significantly reduce industrial production costs and generate new jobs in modern industry on a global scale. Promising examples are in quantum computing: One requirement in quantum computing is the fast initialization of qubitstates. As coherence times are approaching the millisecond regime, the conventional passive initialization protocol by waiting takes a too large fraction of the overall computing time. This project contributes a versatile tool for in-situ initialization of qubits in large-scale quantum computers. Due to its exponential speedup, the quantum computer itself may revolutionize pharmaceuticals, telecommunication, and financial services.

The overall objectives of this proposal are to realize noise-enhanced quantum control using transmon qubits with tunable decoherence rates in circuit QED setups. The ideas are based on two important objectives, which are implemented in QCD Labs at Aalto University, having strong experience in SET: The first objective is to realize a single qubit with tunable decoherence rates. This objective enables new quantum computing applications by realizing a fast qubit reset and explores new physics by investigating non-Markovian qubit dynamics. The second objective is to use the tunable coupling between two of these qubits to build the unit cell of a fully controllable Ising model. This objective is used to study remote-cooling of one qubit via the other and to simulate multi-dimensional master equations.

In conclusion, the proposed actions have been achieved to an extent possible considering the fact that the project was ended after 13 months instead of 24 months. We have published 7 peer-reviewed scientific articles, organized a research stay at ETH Zurich, instructed 8 students, created 3 videos for dissemination, participated in conferences, were mentioned in 10 newspaper articles, became member of 3 physical societies, referee for 2 scientific journals, and participated in 4 vocational trainings. We have applied for a docentship a Aalto University, which was successfully granted to the fellow after the end of this project. The reason for the termination of the project was that the fellow and the supervisor of this project have spin-out a company from Aalto University, which meanwhile is the leading European company for quantum computing: IQM Finland Oy.
We have established fabrication processes for superconducting qubits which are compatible with the integration of SET devices to control and readout qubits at the quantum level. We have developed a new and faster method to readout superconducting qubits (Ikonen, Goetz, et al. PRL 2019). We have performed experiments with superconducting resonators coupled to SET devices. In these experiments, we have studied two fundamental process that are controlled by noise and dissipation. First, we have studied the broadband Lamb shift of a superconducting resonator (Silveri, Goetz, et al. Nature Physics 2019). Second, we have optimized the heat flow between two superconducting elements using exceptional points (Partanen, Goetz, et al. PRB 2019). We have developed techniques to use noise as precisely calibrated power sources (Hyyppä, Goetz, et al. APL 2019). Finally, we have experimentally demonstrated the fast reset of a quantum circuit when coupled to an SET device (Sevriuk, Goetz, et al. APL 2019).

The main exploitation of the results are that we have created a spin-out company, IQM Finland Oy, using methods developed in this project to develop large-scale quantum computers. Meanwhile, the company has become the leading European supplier for hardware in superconducting quantum computing. The technology and processes created in this project and the fabrication and experimental methods developed in this project were a major part of the technology transfer during the spin-out process.

The dissemination of the results was achieved in various forms: We have organized a visit to the group of A. Wallraff at ETH Zurich during June 2018. We have participated in the 69th Lindau Nobel Laureate Meetings and provided a master class together with the Laureates Serge Haroche and Dave Wineland. In September 2018, we have presented our research ideas during Falling Walls Lab event in Brussels. In July 2018, we have had a participation in the EuroScience Open Forum - ESOF 2018 Toulouse. In addition, we have participated in several scientific conferences.

We have been disseminating our research through video channels, for example: Why ultra cold computers hold quantum secrets (14.03.2019) YouTube video; QCD Labs in a nutshell (26.02.2019) Vimeo video; How to speed up getting data from a quantum computer (25.02.2019) YouTube video;

Further dissemination was achieved through newspaper articles, for examples:
Quantum physicists at Aalto University succeed in controlling energy losses and shifts (04.04.2019) Science Business; United Kingdom; Faster method to read quantum memory (25.02.2019) Science Daily, United States.
Scientists developed a faster method to read quantum memory (25.02.2019) Tech Explorist.
The projected has generated scientific results that go beyond the state of the art having strong scientific impact. After the project was terminated, further research was conducted to demonstrate the technical potential of the quantum circuits developed in this project. The biggest socio-economic impact of the project was that it has contributed significantly to the spin-out process of IQM Finland Oy. This spin-out attracted a total of EUR 11.45 Mio from private investors to commercialize the technology developed partly in this project. Meanwhile, the fellow is leading IQM Finland as CEO, which is the largest European effort to build a quantum computer with currently 36 full-time employees. IQM has in March opened its first subsidiary in Munich to start a global expansion plan.
Artistic view of the Broadband Lamb shift studied in this project (Figure credit: Heikka Valja).