Joonas Peltonen

Correlated Emission Lasing in Harmonic Oscillators Coupled via a Single Three-Level Artificial Atom.

A single superconducting artificial atom can be used for coupling electromagnetic fields up to the single-photon level due to an easily achieved strong coupling regime. Bringing a pair of harmonic oscillators into resonance with the transitions of a three-level atom converts atomic spontaneous processes into correlated emission dynamics. We present the experimental demonstration of two-mode correlated emission lasing in harmonic oscillators coupled via a fully controllable three-level superconducting quantum system (artificial atom). The correlation of emissions with two different colors reveals itself as equally narrowed linewidths and quenching of their mutual phase diffusion. The mutual linewidth is more than 4 orders of magnitude narrower than the Schawlow-Townes limit. The interference between the different color lasing fields demonstrates that the two-mode fields are strongly correlated.

Tunable photonic heat transport in a quantum heat valve

Quantum thermodynamics is emerging both as a topic of fundamental research and as a means to understand and potentially improve the performance of quantum devices1–10. A prominent platform for achieving the necessary manipulation of quantum states is superconducting circuit quantum electrodynamics (QED)11. In this platform, thermalization of a quantum system12–15 can be achieved by interfacing the circuit QED subsystem with a thermal reservoir of appropriate Hilbert dimensionality. Here we study heat transport through an assembly consisting of a superconducting qubit16 capacitively coupled between two nominally identical coplanar waveguide resonators, each equipped with a heat reservoir in the form of a normal-metal mesoscopic resistor termination. We report the observation of tunable photonic heat transport through the resonator–qubit–resonator assembly, showing that the reservoir-to-reservoir heat flux depends on the interplay between the qubit–resonator and the resonator–reservoir couplings, yielding qualitatively dissimilar results in different coupling regimes. Our quantum heat valve is relevant for the realization of quantum heat engines17 and refrigerators, which can be obtained, for example, by exploiting the time-domain dynamics and coherence of driven superconducting qubits18,19. This effort would ultimately bridge the gap between the fields of quantum information and thermodynamics of mesoscopic systems.The state of a superconducting circuit qubit governs the photonic heat flow through an integrated assembly, constituting a quantum heat valve that provides a testbed for exploring quantum thermodynamics in a circuit quantum electrodynamics setting.

Noise of a superconducting magnetic flux sensor based on a proximity Josephson junction

We demonstrate simultaneous measurements of DC transport properties and flux noise of a hybrid superconducting magnetometer based on the proximity effect (superconducting quantum interference proximity transistor, SQUIPT). The noise is probed by a cryogenic amplifier operating in the frequency range of a few MHz. In our non-optimized device, we achieve minimum flux noise ~4u2009μΦ0/Hz1/2, set by the shot noise of the probe tunnel junction. The flux noise performance can be improved by further optimization of the SQUIPT parameters, primarily minimization of the proximity junction length and cross section. Furthermore, the experiment demonstrates that the setup can be used to investigate shot noise in other nonlinear devices with high impedance. This technique opens the opportunity to measure sensitive magnetometers including SQUIPT devices with very low dissipation.

Hybrid rf SQUID qubit based on high kinetic inductance

We report development and microwave characterization of rf SQUID (Superconducting QUantum Interference Device) qubits, consisting of an aluminium-based Josephson junction embedded in a superconducting loop patterned from a thin film of TiN with high kinetic inductance. Here we demonstrate that the systems can offer small physical size, high anharmonicity, and small scatter of device parameters. The work constitutes a non-tunable prototype realization of an rf SQUID qubit built on the kinetic inductance of a superconducting nanowire, proposed in Phys. Rev. Lett. 104, 027002 (2010). The hybrid devices can be utilized as tools to shed further light onto the origin of film dissipation and decoherence in phase-slip nanowire qubits, patterned entirely from disordered superconducting films.

Magnetometry with Low-Resistance Proximity Josephson Junction

We characterize a niobium-based superconducting quantum interference proximity transistor (Nb-SQUIPT) and its key constituent formed by a Nb–Cu–Nb SNS weak link. The Nb-SQUIPT and SNS devices are fabricated simultaneously in two separate lithography and deposition steps, relying on Ar ion cleaning of the Nb contact surfaces. The quality of the Nb–Cu interface is characterized by measuring the temperature-dependent equilibrium critical supercurrent of the SNS junction. In the Nb-SQUIPT device, we observe a maximum flux-to-current transfer function value of about

Filtering random telegraph signal

55;mathrm {nA}/mathrm {Phi }_0

The XLIII Annual Conference of the Finnish Physical Society (Physics Days 2009), Espoo, Finland, 12-14 March

55nA/Φ0 in the sub-gap regime of bias voltages. This results in suppression of power dissipation down to a few fW. Low-bias operation of the device with a relatively low probe junction resistance decreases the dissipation by up to two orders of magnitude compared to a conventional device based on an Al–Cu–Al SNS junction and an Al tunnel probe (Al-SQUIPT).