The famed p-wave superconductivity harbors a variety of exotic topological states. The practical ways for its implementing are being extensively discussed in literature, and the contact of a superconductor with the topological insulator is expected to become the most promising candidate. There have been reports of the 4π-periodicity in such contacts, which are a hallmark of the p-wave...
Transport measurements of the superconductor-insulator transition (SIT) in disordered two-dimensional films and Josephson junction arrays showed the existence of an anomalous metallic phase that persists to low temperatures. The nature of this mysterious phase often referred to as “Bose metal,” remains unclear. We develop a gauge theory of the Bose metal as the phase in which Cooper pairs and...
Recent interest in the effect of intrinsic spin-orbit coupling in materials that exhibit an excitation gap has led to the notions of topological insulators and topological superconductors. Intrinsic spin-orbit coupling is enhanced in non-centrosymmetric materials, as in this case already band-diagonal matrix elements contribute. We study non-centrosymmetric superconductors with various point...
Quantum dynamics is very sensitive to dimensionality. While two-dimensional electronic systems form Fermi liquids, one-dimensional systems - Tomonaga-Luttinger liquids - are described by purely bosonic excitations, even though they are initially made of fermions.
With the advent of coherent single-electron sources [1- 3], the quantum dynamics of such a liquid is now accessible at the...
The scanning tunneling microscope (STM) allows for a rather unique control over matter at atomic scale. By measuring at very low temperatures, it also serves as a spectroscopic probe of low energy phenomena, such as superconductivity. As such, the STM can measure all known features of superconducting tunneling, namely density of states, inelastic tunneling, Andreev scattering and Josephson...
In 1964 V. L. Ginzburg predicted that new superconducting phases could appear in ultrathin films deposited on insulating surfaces. In 2010 superconductivity below 2K was discovered in some crystalline atomic monolayers of Pb grown on atomically clean Si(111) [1,2]. Owing their peculiar electronic properties, these two-dimensional materials manifest a number of intriguing superconducting...
Study of topological matter is one of the fascinating main roads of modern physics. The present overview is aimed at topology- and geometry-driven effects, owing to special geometries of novel micro- and nanoarchitectures fabricated of both conventional and topologically nontrivial materials implemented by the high-tech techniques, in particular, self-organization [1, 2]. I will demonstrate...
We work out a unified theory describing both nonlocal electron transport and cross-correlated shot noise in a three-terminal normal-superconducting-normal (NSN) hybrid nanostructure. We describe noise cross correlations both for subgap and overgap bias voltages and for arbitrary distribution of channel transmissions
in NS contacts. We specifically address a physically important situation of...
Josephson coupling between superconducting and ferromagnetic layers is driving new fundamental physics and innovative applications for superconducting electronics and quantum circuits [1,2]. Examples are: the possibility to switch the ground state of a Josephson junction (JJ) from a 0 to a π phase state, the existence of JJs having a doubly degenerate ground state with an average Josephson...
Short ballistic graphene Josephson junctions (GJJ) sustain superconducting current with a strongly non-sinusoidal current-phase relation (CPR) up to a critical current threshold. The CPR, arising from proximitized superconductivity, is gate-voltage tunable and exhibits peculiar skewness observed in high-quality graphene-superconductors heterostructures with clean interfaces. These properties...
Ferromagnetic Josephson junctions present a rich emerging physics due to the coupling between ferromagnetism and superconductivity. The interplay between the two competing phases causes an oscillation of the superconducting order parameter within the ferromagnetic barrier, which is responsible for the appearance of a π ground state, and of triplet correlations in the Josephson junction [1,2]....
Despite the promises of superconducting qubits, their performance is presently limited by short coherence times due to defects intrinsic to materials. As a result, future quantum computers would require massive error correction circuits, which seem to be very challenging to build. Another more promising path would be to improve this coherence time, which would relax the constraints on the...
Qubit readout is an indispensable element of any quantum information processor. In this work,
we propose an original coupling scheme between a qubit and a cavity mode based on a non-perturbative
cross-Kerr interaction. This scheme, using the same experimental techniques as the perturbative cross-Kerr coupling (dispersive interaction), leads to an alternative readout mechanism for...
Traditionally, the control and measurement of superconducting quantum devices including arrays of qubits are done using room-temperature classical electronics connected to cryogenic environment via high fidelity cables. This poses daunting technical challenges to quantum system scaling as the heat load, latency, noise associated with bringing signals in and out of the cryostat rise...
We report on the experimental observation of spin-dependent thermoelectric effects in superconductor-ferromagnet tunnel junctions in high magnetic fields. The thermoelectric signals are due to a spin-dependent lifting of particle-hole symmetry on the energy scale of the superconducting gap. Due to the small energy scale, the thermoelectric effects can be quite large, and we infer a maximum...
We investigate the properties of gate-tunable single quantum dot junctions, obtained by the electromigration technique, in the spin-1/2 Kondo regime with rather large $U/\Gamma$ ($U$ is the on-site interaction and $\Gamma$ the tunnel coupling). In the first part we investigate the device response in the presence of superconductivity in the leads. We tune the ground state of the dot quantum...
A quantitative theory describing the behaviour of current/voltage characteristics (CVC) and conductances (G) for both s-wave (S) and d-wave (D) type of ballistic voltage-biased superconductor/ferromagnet (F)/superconductor (SFS or DFD) trilayers is developed. The calculation is based on the nonequilibrium microscopic theory of transport in isotropic s-wave superconductor/normal metal...
We study the dynamics of a dissipative Jaynes-Cummings model subject to a strong resonant drive. Above a certain drive threshold there appear two metastable states in the stationary state with roughly the same field amplitude but different phases which are well captured by the bifurcation in the neo-classical approach. Their appearance is associated with the splitting of the spectrum of the...
The Coherent Quantum Phase Slip (CQPS) effect in superconducting nanowires is exactly dual to the Josephson effect – tunneling of Cooper pairs through a thin dielectric layer. CQPS has been experimentally proven for the first time in Ref. [1] and since then reproduced in different materials [2, 3]. CQPS is interesting from the fundamental point of view as well as for practical applications,...
In our talk we present a microscopic theory describing complete statistics of voltage fluctuations generated by quantum phase slips (QPS) in superconducting nanowires. We evaluate the cumulant generating function and demonstrate that shot noise of the voltage as well as the third and all higher voltage cumulants differ from zero only due to the presence of QPS. In the zero-frequency limit...
The Coulomb drag effect arises due to electron-electron interactions, when two metallic conductors are placed in close vicinity to each other. It manifests itself as a charge current or voltage drop induced in one of the conductors, if the current flows through the second one. Often it can be interpreted as an effect of rectification of the non-equilibrium quantum noise of current. Here, we...
We demonstrate the in situ engineering of superconducting nanowires via modulation of material properties through high applied current densities [1]. We show that the sequential repetition of such customized electro-annealing in a niobium nanoconstriction can broadly tune the superconducting critical temperature Tc and the normal-state resistance Rn in the targeted area. Once a sizable Rn is...
Josephson junctions involving a conventional superconductor and an exotic conductor, represented by the surface of a 3D topological insulator (TI), a Dirac semimetal or the edge states of two-dimensional quantum wells, are ideal systems to emulate topological superconductivity characterized by unconventional order parameter (OP), with an orbital component assuming the form of a chiral px + ipy...
Two dimensional electron systems (2DES) formed at the interface between insulating transition metal oxides have demonstrated an extraordinary range of properties. The coexistence among these properties can be studied vie electric field effect, making these systems an ideal test bench for the investigation of novel quantum phenomena.
A notable example is the coexistence between...
The geometrical structure of the Hilbert space continues to receive a lot of attention. The Fubini-Study metric tensor of the Hilbert space, also referred to as Fisher information metric, provides a natural measure of distance in the Hilbert space, related to quantum fidelity – a fundamental concept in quantum information science. Interestingly, the concepts of the Fubini-Study metric tensor...
Quantum annealing (QA) is getting more and more relevant as powerful solver of optimization problems. Thanks to the availability of“commercial”adiabatic quantum computers, based on QA, there is plenty of proposals both on the fundamental and on the applied side. In QA a target ground state encodes the solution of a computationally hard problem. Such ground state is approached exploring the...
Ultrastrong coupling (USC) between light and matter has been recently achieved in erchitectures of solid state artificial atoms coupled to cavities. They may provide new building blocks for quantum state processing, where ultrafast quantum gates can be performed thus meeting the requirements for fault-tolerant quantum computation.
However it has been shown [1] that in the USC regime the...
A quantum phase transition (QPT) represents a discontinuous change of the ground state of an extended, ideally infinite, system. Such transitions occur at zero temperature and they are driven by tuning a parameter in the Hamiltonian. If an effective Hamiltonian is such that it includes some temperature-dependent parameters, then a temperature-controlled quantum transition (TC-QPT) can be...
Quantum behavior of superconducting nanowires may essentially depend on the employed experimental setup. Here we investigate a setup that enables passing equilibrium supercurrent across an arbitrary segment of the wire without restricting fluctuations of its superconducting phase. The low temperature physics of the system is determined by a combined effect of collective sound-like plasma...
Al low temperatures superconducting nanowires demonstrate wide range of intriguing physical phenomena. Of particular interest are those that are due to quantum phase slips (QPS), as an example the change in nonlocal transport in superconducting nanowires. This work is devoted to studying the interplay between Coulomb drag effect and QPS in a system of coupled superconducting nanowires. It is...
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter [1]. Fundamental attributes of superconductivity such as zero resistivity, persistent currents in closed loops, energy gap in excitation spectra can be drastically violated by fluctuations....
