QUROPE Quantum Information Processing and Communication in Europe

M. Van den Nest
Phyical Review Letters 110, 060504 (2013)

It is strongly expected that quantum computers will offer an exponential computation advantage over their
classical counterparts. It is therefore a fundamental problem to understand what aspect or aspects of quantum
mechanics are responsible for this improvement, which remains largely unsolved. A natural candidate is the
entanglement present in quantum mechanics as the source of the computation power, however there is no
decisive evidence that the answer actually lies there.

A. Stute, B. Casabone, B, Brandstätter, K. Friebe, T. E. Northup and R. Blatt
Nature Photonics 7, 219-222 (2013)

Photonic Boson Sampling in a Tunable Circuit
M. A. Broome, A. Fedrizzi, S. Rahimi-Keshari, J. Dove, S. Aaronson, T. C. Ralph and A. G. White
Science 339, 794-798 (2013) and

Integrated multimode interferometers with arbitrary designs for photonic boson sampling
A. Crespi, R. Osellame, R. Ramponi, D. J. Brod, E. F. Galvao, N. Spagnolo, C. Vitelli, E. Maiorino, P. Mataloni and F. Sciarrino
Nature Photonics 7, 545-549 (2013) and

On the 22nd of January 2014, Neelie KROES, the current Vice-President of the European Commission and responsible for the Digital Agenda, delivered a speech entitled "A vision for Europe" at the World Economic Forum held in Davos.

We present a scheme for the dissipative preparation of an entangled steady state of two superconducting qubits in a circuit quantum electrodynamics (QED) setup. Combining resonator photon loss—a dissipative process already present in the setup—with an effective two-photon microwave drive, we engineer an effective decay mechanism which prepares a maximally entangled state of the two qubits. This state is then maintained as the steady state of the driven, dissipative evolution.

Specific challenge: Devices that exploit quantum phenomena such as superposition and entanglement have the potential to enable radically new technologies. Several promising directions are now well known, for instance in quantum computation and simulation, quantum communication, quantum metrology and sensing. However, overcoming basic scientific challenges as well as bridging from the scientific results to concrete engineering technologies has proved difficult.

In a recent publication in Scientific Reports the group led by SOLID partner Jonathan Finley at the Walter Schottky institut of TUM achieve fast, all optical spin control in a single quantum dot without magnetic fields.

In a recent publication in Physical Review Letters the TU-Delft group led by SOLID partner Leo DiCarlo demonstrated an indirect partial measurement of a transmon qubit in circuit quantum electrodynamics.  This was don by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allowed the group to show how it is possible to tailor the measurement strength and operator.

IThe SOLID group of Lieven Vandersypen recently published a paper in Physical Review Letters in which they investigated phonon-induced spin and charge relaxation mediated by spin-orbit and hyperfine interactions for a single electron confined within a double quantum dot. They extract an electron spin relaxation rate that varies nonmonotonically with the detuning between the dots and confirm this model with experiments performed on a GaAs double dot.

The Quantronics group at SOLID partner CEA have recently published a paper in Physical Review Letters in wihch they measure the quantum fluctuations of a pumped nonlinear resonator using a superconducting artificial atom as an in situ probe. The qubit excitation spectrum provided access to the frequency and amount of excitation of the intracavity field fluctuations, from which we infer its effective temperature.