54 citations · 221 across the 15 of their papers we have counts for
9 papers · 1 filter
Multiplying and detecting propagating microwave photons using inelastic Cooper-pair tunneling
Juha Leppäkangas, Michael Marthaler, Dibyendu Hazra +5
The interaction between propagating microwave fields and Cooper-pair tunneling across a DC voltage-biased Josephson junction can be highly nonlinear. We show theoretically that thi…
Creating photon-number squeezed strong microwave fields by a Cooper-pair injection laser
Martin Koppenhöfer, Juha Leppäkangas, Michael Marthaler
The use of artificial atoms as an active lasing medium opens a way to construct novel sources of nonclassical radiation. An example is the creation of photon-number squeezed light.…
Correlated Cooper pair transport and microwave photon emission in the dynamical Coulomb blockade
Juha Leppäkangas, Mikael Fogelström, Michael Marthaler +1
We study theoretically electromagnetic radiation emitted by inelastic Cooper-pair tunneling. We consider a dc-voltage-biased superconducting transmission line terminated by a Josep…
Diagrammatic description of a system coupled strongly to a bosonic bath
Michael Marthaler, Juha Leppäkangas
We study a system-bath description in the strong coupling regime where it is not possible to derive a master equation for the reduced density matrix by a direct expansion in the sy…
Fully superconducting Bloch-oscillating transistor: Amplification and bifurcation based on Bloch oscillations and counterflowing Cooper pairs
J. Leppäkangas, A. Puska, L. Äkäslompolo +2
The Bloch-oscillating transistor (BOT) is an amplifier that utilizes semiclassical dynamics of states in energy bands under traveling quasimomentum. In a BOT, a single quasiparticl…
Nonclassical photon pair production in a voltage-biased Josephson junction
Juha Leppäkangas, Göran Johansson, Michael Marthaler +1
We investigate electromagnetic radiation emitted by a small voltage-biased Josephson junction connected to a superconducting transmission line. At frequencies below the well known…
Sub-Poissonian photon statistics in a strongly coupled single-qubit laser
M. Marthaler, Pei-Qing Jin, Juha Leppäkangas +1
We investigate qubit lasing in the strong coupling limit. The qubit is given by a Cooper-pair box, and population inversion is established by an additional third state, which can b…
Fragility of multi-junction flux qubits against quasiparticle tunneling
Juha Leppäkangas, Michael Marthaler
We study decoherence in superconducting qubits due to quasiparticle tunneling which is enhanced by two known deviations from the equilibrium BCS theory. The first process correspon…
Phase-dependent quasiparticle tunneling in Josephson junctions: Measuring the cos-phi term with a superconducting charge qubit
Juha Leppäkangas, Michael Marthaler, Gerd Schön
We investigate quasiparticle tunneling in a Cooper-pair box which is embedded in a superconducting ring to allow control of the total phase difference across the island. The phase…