2020: Year in Review at Qudev

It was an unusual year for the Quantum Device Lab (@Qudev) at ETH Zurich (@ETH_en). Despite the long and continuing struggle with the implications of a pandemic, the lab and its members did hold on extremely well and did great research.

A good start into 2020

We started out the year with publishing work by Jean-Claude Besse on detecting the parity of propagating microwave radiation fields in a quantum non demolition fashion in a paper entitled Parity Detection of Propagating Microwave Fields (J. - C. Besse, S. Gasparinetti, M. C. Collodo, T. Walter, A. Remm, J. Krause, C. Eichler, and A. Wallraff) in Phys. Rev. X10, 011046 (2020) [open access arXiv:1912.09896]. This detector allows to project propagating coherent states into states with even or odd photon number only, i.e. realizing propagating Schrodinger cat states.

At the end of 2019 the Quantum Device Lab performed work toward realizing the quantum error detection with superconducting circuits using a distance-two surface code composed of four data qubits and three ancilla qubits used for detecting errors by performing gate-based parity measurements on the data qubits in the seven-qubit device shown below.

This seven-qubit device was mounted in our custom sample holder allowing for up to 48 ports and installed in a Bluefors cryogenic system. The experiments were performed using Zurich Instruments hardware both for controlling the qubits and for reading out their quantum state. The paper was published as Repeated Quantum Error Detection in a Surface Code, (C. Kraglund Andersen, A. Remm, S. Lazar, S. Krinner, N. Lacroix, G. J. Norris, M. Gabureac, C. Eichler, and A. Wallraff) in Nature Physics 16, 875–880 (2020) [open access arXiv:1912.09410]. The same sample and setup were used for two more experiments performed and finalized in 2020.

Unexpected changes

In the beginning of march it became clear that Switzerland was being struck by the pandemic particularly hard. As a result, ETH Zurich did switch rapidly to online teaching and also limited access to the labs to a bare minimum. While this shutdown seriously affected the experimental work in our lab and prohibited any fabrication of devices, we were in the fortunate situation of being able to run two of our large quantum computing setups fully remotely (see photo below). We also had quite a few pieces of our research work at a good stage for writing up the results. Therefore, the lab as a whole did get through the first lock-down in surprisingly good shape.

Excellent progress, despite the constraints

For example, we were fortunate enough to finalize our first experiment on quantum state transfer between superconducting circuits housed in two crysotates separated by a 5-meter-long cryogenic link, which also allowed for entangling the two circuits with each other, before the lock-down. We presented these results for the first time at an improvised version of the APS march meeting, which was cancelled due to the pandemic on the morning that five of our lab members were stepping out of our homes to get on flights to Denver.

This exciting work, supported by an ERC Advanced Grant was reported in a publication written up during the lock-down period and published recently as Microwave Quantum Link between Superconducting Circuits Housed in Spatially Separated Cryogenic Systems (P. Magnard, S. Storz, P. Kurpiers, J. Sch?r, F. Marxer, J. Lütolf, T. Walter, J. - C. Besse, M. Gabureac, K. Reuer, A. Akin, B. Royer, A. Blais, and A. Wallraff) in Phys. Rev. Lett. 125, 260502 (2020) [open access arXiv:2008.0164]. There is coverage of this work on the ETH Zurich website and in the Physics Magazine. Also check out this short video on our work.

The state transfer and entanglement generation protocol between the two cryogenic systems is enabled by controlled exchange of single photons between the two cryostats, which is based on the longstanding research of our lab on quantum optics with superconducting circuits.

In a similar vein, we have continued our work on photon sources and detectors for Realizing a Deterministic Source of Multipartite-Entangled Photonic Qubits (J. - C. Besse, K. Reuer, M. C. Collodo, A. Wulff, L. Wernli, A. Copetudo, D. Malz, P. Magnard, A. Akin, M. Gabureac, G. J. Norris, J. I. Cirac, A. Wallraff, and C. Eichler) published in Nat. Commun. 11, 4877 (2020) [open access arXiv:2005.07060]. This work allowed us to realize and characterize GHZ, W and cluster states with up to 10 photons (or modes, if you are picky about the language).

We have performed two further experiments on our seven-qubit device. One in which we improved the performance of deep quantum approximate optimization algorithms (QAOA) using an optimized gate set with controllable conditional phase, Improving the Performance of Deep Quantum Optimization Algorithms with Continuous Gate Sets (N. Lacroix, C. Hellings, C. Kraglund Andersen, A. Di Paolo, A. Remm, S. Lazar, S. Krinner, G. J. Norris, M. Gabureac, J. Heinsoo, A. Blais, C. Eichler, and A. Wallraff) PRX Quantum 1, 110304 (2020) [open access arXiv:2005.05275] with an ETH Master student as a lead author.

And a second experiment in which we carefully analyzed the role of so-called spectator qubits on coherent errors in two-qubit gates, Demonstration of an All-Microwave Controlled-Phase Gate between Far-Detuned Qubits, S. Krinner, P. Kurpiers, B. Royer, P. Magnard, I. Tsitsilin, J. - C. Besse, A. Remm, A. Blais, and A. Wallraff, Phys. Rev. Appl. 14, 044039 (2020), open access arXiv:2006.10639.

A great year for Qudev alumni on the faculty job market

In 2020, four current members or recent alumni of the Quantum Device Lab started or secured their faculty positions. These include Stefan Filipp, who is now a full professor at the TU Munich and the WMI of the Bavarian Academy of Sciences (WMI-quantum website), Pasquale Scarlino, who started as a tenure-track Assistant Professor at our sister school EPF Lausanne (press release), Simone Gasparinetti, who was promoted to tenure-track Assistant Professor at Chalmers University (web link), and another offer was just accepted.

They join eight Qudev alumni, who are on the faculty at Stanford, Chicago, Oxford, IST Austria, Leiden, UQ Brisbane, IACS Kolkata and Paris Saclay and those working at Rigetti, IQM, Zurich Instruments, Bosch, ABB, Sensirion, Rhode&Schwarz, Radionor, Microsoft and others.

Work lead by collaborators

We have also contributed to a number of publications lead by collaborators or former postdocs of our Quantum Device Lab. Check these papers out by following the links:

Radiative cooling of a spin ensemble, B. Albanese, S. Probst, V. Ranjan, C. W. Zollitsch, M. Pechal, A. Wallraff, J. J. L. Morton, D. Vion, D. Esteve, E. Flurin, and P. Bertet, Nature Physics (2020), open access arXiv:1910.11092

Strong photon coupling to the quadrupole moment of an electron in a solid-state qubit, J. V. Koski, A. J. Landig, M. Russ, J. C. Abadillo-Uriel, P. Scarlino, B. Kratochwil, C. Reichl, W. Wegscheider, G. Burkard, M. Friesen, S. N. Coppersmith, A. Wallraff, T. Ihn, and K. Ensslin, Nature Physics (2020), open access arXiv:1905.00846

Primary Thermometry of Propagating Microwaves in the Quantum Regime, M. Scigliuzzo, A. Bengtsson, J. - C. Besse, A. Wallraff, P. Delsing, and S. Gasparinetti, Phys. Rev. X 10, 041054 (2020), open access arXiv:2003.13522

Looking forward

In 2021, we are looking forward to continue our work on scaling up superconducting circuits for quantum information processing. We are well set for performing experiments with a larger number of qubits ...

... and experiments with a quantum link extended to 30 meters of distance, which is in the final stages of assembly.

If you are up for it, check out the video version of our review.

We are looking forward to a successful new year 2021 for our students, postdocs, staff, collaborators and friends.

And of course, like every one else we hope that life will get a bit more normal again in the coming year.

All the best and stay healthy and safe!

Andreas Wallraff

for the team of the Quantum Device Lab.