Dr. Markus Jerger

After a two-semester peek at computer science while still in high school, Markus decided that physics was the more exciting subject to study. A few years later, he received his Diplom in physics from the University of Karlsruhe in Germany, for theoretical work on geometric phases in charge and spin pumping. Seeking a more hands-on experience, he went to pursue a PhD in experimental quantum physics at the Karlsruhe Institute of Technology, working on multiplexed readout of superconducting artificial atoms. After finishing his PhD in 2013, he became the first member of Arkady Fedorov's group at the University of Queensland. In Arkady's lab, Markus is responsible for everything analog and digital, particularly measurement soft-, hard-, and firmware for microwave frequency systems.

2017

We experimentally realize a quantum random number generator (QRNG) with randomness of each generated number certified by the Kochen-Specker theorem. Employing this novel certification scheme eliminates the necessity for input seed random numbers and lifts the non-locality requirement for the certified QRNG. Implementation on the base of superconducting qubits allows achieving a bit rate of 25 kBit/s, two orders of magnitude higher than previously reported certified QRNGs. These improvements make our result a major step towards realization a practical certified quantum QRNG with implications for digital security and modelling algorithms.

Jerger M., Vasselin Z. and Fedorov A., 2017
arXiv:1706.05829

We present a technique to measure the transfer function of a control line using a qubit as a vector network analyzer. Our method requires coupling the line under test to the the longitudinal component of the Hamiltonian of the qubit and the ability to induce Rabi oscillations through simultaneous driving of the transversal component. We used this technique to characterize the 'flux' control of a superconducting Transmon qubit in the range of 8 to 400\,MHz. Our method can be used for the qubit 'flux' line calibration to increase the fidelity of entangling gates for the quantum processor. The qubit can be also used as a microscopic probe of the electro-magnetic fields on a chip. 

2016

The ability to determine whether a multi-level quantum system is in a certain state while preserving quantum coherence between all orthorgonal states is necessary to realize binary-outcome compatible measurements which are, in turn, a prerequisite for testing the contextuality of quantum mechanics. In this paper, we use a three-level superconducting system (a qutrit) coupled to a microwave cavity to explore different regimes of quantum measurement. In particular, we engineer the dispersive shifts of the cavity frequency to be identical for the first and second excited states of the qutrit which allows us to realize a strong projective binary-outcome measurement onto its ground state with a fidelity of 94.3%. Complemented with standard microwave control and low-noise parametric amplification, this scheme can be used to create sets of compatible measurements to reveal the contextual nature of superconducting circuits. 

Woolley M. J. et al, 2016
Phys. Rev. B, 93, pp. 224518

Resonant coupling of a Quartz nanoresonator to a superconducting qubit has provided the first observation of a macroscopic mechanical degree of freedom in its quantum ground state. However, unlike nano-oscillators, macroscopic quartz oscillators such as Bulk Acoustic Wave (BAW) oscillators offer exceptional mechanical properties including large effective masses, high frequencies, and extremely high quality factors. This makes them an attractive platform not only for the pursuit of quantum optics experiments with phonons, but also for tests of the limits of quantum mechanics itself gravitational wave detection, and tests of Lorentz symmetry. On other hand, their large geometric size makes coupling to them challenging. Most critically, large unavoidable stray capacitance between the BAW oscillator electrodes reduces the amplitude of the oscillating voltage, and the corresponding coupling strength to electrical circuits becomes impractically small. Our theoretical paper studies the scheme which can bust coupling to a such a resonator to achieve and detect the ground state of its mechanical degree of freedom.

Reshitnyk Y., Jerger M. and Fedorov A., 2016
EPJ Quantum Technol., 3, 1, pp. 1-6

Three-dimensional (3D) microwave cavities with embedded superconducting quantum bits (qubits), provide a popular and versatile platform for quantum information processing and hybrid quantum systems. A current issue that has arisen is that 3D superconducting cavities do not permit magnetic field control of qubits embedded in these cavities. In contrast, microwave cavities made of normal metals can be transparent to magnetic fields, but experience a much lower quality factor, which negates many of the advantages of the 3D architecture. Here we presented measurements of a device that bridges a gap between these two types of cavities with magnetic field control and an order of magnitude higher quality factor compared to all previously tested copper cavities. An added benefit to that our hybrid cavity possesses is that it also provides an improved thermal link to the sample that superconducting cavities alone cannot provide. A large improvement in quality factor and magnetic field control makes this 3D hybrid cavity an attractive new platform for circuit quantum electrodynamics experiments.

Jerger M. et al, 2016
Nature Communications, 7, pp. 12930

Contextuality is one of the most fundamental properties of quantum mechanics, distinguishing it from classical physics without a need for nonlocality or entanglement. It is also a critical resource for exponential speedup in universal surface-code quantum computing. Our result is the first experiment violating a noncontextuality inequality with an indivisible system where entanglement cannot be defined which also addresses all known major loopholes, such as the detection, compatibility and individual-existence loopholes. Violating noncontextuality with superconducting circuits, a leading candidate for implementing surface-code quantum computing, comprises an important conceptual milestone in demonstrating their suitability for quantum technological applications.

The ARC Centre of Excellence for Engineered Quantum Systems

This Centre of Excellence seeks to initiate the Quantum Era in the 21st century by engineering designer quantum systems.