Searcharxiv⌕ Search

arXiv subjects

V. P. Michal

Publications and source records attributed to V. P. Michal.

13 recordsLinked to original sources
arXiv2023

Tunable hole spin-photon interaction based on g-matrix modulation

We consider a spin circuit-QED device where a superconducting microwave resonator is capacitively coupled to a single hole confined in a semiconductor quantum dot. Thanks to the strong spin-orbit coupling intrinsic to valence-band states, the gyromagnetic g-matrix of the hole can be modulated electrically. This modulation couples the photons in the resonator to the hole spin. We show that the applied gate voltages and the magnetic-field orientation enable a versatile control of the spin-photon interaction, whose character can be switched from fully transverse to fully longitudinal. The longitudinal coupling is actually maximal when the transverse one vanishes and vice-versa. This "reciprocal sweetness" results from geometrical properties of the g-matrix and protects the spin against dephasing or relaxation. We estimate coupling rates reaching ~ 10 MHz in realistic settings and discuss potential circuit-QED applications harnessing either the transverse or the longitudinal spin-photon interaction. Furthermore, we demonstrate that the g-matrix curvature can be used to achieve parametric longitudinal coupling with enhanced coherence.

cond-mat.mes-hall↗
arXiv2022

A single hole spin with enhanced coherence in natural silicon

Semiconductor spin qubits based on spin-orbit states are responsive to electric field excitation allowing for practical, fast and potentially scalable qubit control. Spin-electric susceptibility, however, renders these qubits generally vulnerable to electrical noise, which limits their coherence time. Here we report on a spin-orbit qubit consisting of a single hole electrostatically confined in a natural silicon metal-oxide-semiconductor device. By varying the magnetic field orientation, we reveal the existence of operation sweet spots where the impact of charge noise is minimized while preserving an efficient electric-dipole spin control. We correspondingly observe an extension of the Hahn-echo coherence time up to 88 $μ$s, exceeding by an order of magnitude the best reported values for hole-spin qubits, and approaching the state-of-the-art for electron spin qubits with synthetic spin-orbit coupling in isotopically-purified silicon. This finding largely enhances the prospects of silicon-based hole spin qubits for scalable quantum information processing.

cond-mat.mes-hall↗
arXiv2019

Interaction without back-action in the context of quantum manipulation

We address the interaction between two quantum systems (A and B) that is mediated by their common linear environment. If the environment is out of equilibrium the resulting interaction violates Onsager relations and cannot be described by a Hamiltonian. In simple terms the action of system A on system B does not necessarily produce a back-action. We derive general quantum equations describing the situation and analyze in details their classical correspondence. Changing the properties of the environment one can easily change and engineer the resulting interaction. It is tempting to use this for quantum manipulation of the systems. However the resulting quantum gate is not always unitary and may induce a loss of quantum coherence. For a relevant example we consider systems A and B to be spins of arbitrary values and arrange the interaction to realize an analogue of the two-qubit CNOT gate. The direction of spin A controls the rotation of spin B while spin A is not rotated experiencing no back-action from spin B. We solve the quantum dynamics equations and analyze the purity of the resulting density matrix. The resulting purity essentially depends on the initial states of the systems. We attempt to find a universal characteristics of the purity optimizing it for the worst choice of initial states. For both spins $s_A=s_B=1/2$, the optimized purity is bounded by 1/2 irrespective of the details of the gate. We also study in detail the semiclassical limit of large spins. In this case the optimized purity is bounded by $(1+π/2)^{-1}\approx0.39$. This is much better than the typical purity of a large spin state $\sim s^{-1}$. We conclude that although the quantum manipulation without back-action inevitably causes decoherence of the quantum states the actual purity of the resulting state can be optimized and made relatively high.

cond-mat.mes-hall↗
arXiv2018

Finite temperature disordered bosons in two dimensions

We study phase transitions in a two dimensional weakly interacting Bose gas in a random potential at finite temperatures. We identify superfluid, normal fluid, and insulator phases and construct the phase diagram. At T=0 one has a tricritical point where the three phases coexist. The truncation of the energy distribution at the trap barrier, which is a generic phenomenon in cold atom systems, limits the growth of the localization length and in contrast to the thermodynamic limit the insulator phase is present at any temperature.

cond-mat.dis-nn↗
arXiv2017

Non-linear and dot-dependent Zeeman splitting in GaAs/AlGaAs quantum dot arrays

We study the Zeeman splitting in lateral quantum dots that are defined in GaAs-AlGaAs het- erostructures by means of split gates. We demonstrate a non-linear dependence of the splitting on magnetic field and its substantial variations from dot to dot and from heterostructure to het- erostructure. These phenomena are important in the context of information processing since the tunability and dot-dependence of the Zeeman splitting allow for a selective manipulation of spins. We show that spin-orbit effects related to the GaAs band structure quantitatively explain the ob- served magnitude of the non-linear dependence of the Zeeman splitting. Furthermore, spin-orbit effects result in a dependence of the Zeeman splitting on predominantly the out-of-plane quantum dot confinement energy. We also show that the variations of the confinement energy due to charge disorder in the heterostructure may explain the dependence of Zeeman splitting on the dot position. This position may be varied by changing the gate voltages which leads to an electrically tunable Zeeman splitting.

cond-mat.mes-hall↗
arXiv2015

Finite-Temperature Fluid-Insulator Transition of Strongly Interacting 1D Disordered Bosons

We consider the many-body localization-delocalization transition for strongly interacting one- dimensional disordered bosons and construct the full picture of finite temperature behavior of this system. This picture shows two insulator-fluid transitions at any finite temperature when varying the interaction strength. At weak interactions an increase in the interaction strength leads to insulator->fluid transition, and for large interactions one has a reentrance to the insulator regime.

cond-mat.dis-nn↗
arXiv2014

Delocalization of weakly interacting bosons in a 1D quasiperiodic potential

We consider weakly interacting bosons in a 1D quasiperiodic potential (Aubry-Azbel-Harper model) in the regime where all single-particle states are localized. We show that the interparticle interaction may lead to the many-body delocalization and we obtain the finite-temperature phase diagram. Counterintuitively, in a wide range of parameters the delocalization requires stronger cou- pling as the temperature increases. This means that the system of bosons can undergo a transition from a fluid to insulator (glass) state under heating.

cond-mat.dis-nn↗
arXiv2012

Temperature-dependent Ginzburg-Landau parameter

Taking into account both the orbital and the paramagnetic depairing effects we derive a simple analytic formula for the temperature dependence of the Ginzburg-Landau parameter valid in vicinity of field dependent critical temperature in a type-II superconductor.

cond-mat.supr-con↗
arXiv2011

Muon Spin Rotation in Pauli Limited Superconductors

The formalism for analysing the magnetic field distribution in Pauli limited superconductors developed earlier is applied to the field dependence of the vortex lattice static linewidth measured in Muon Spin Rotation ($μ$SR) experiments. In addition to writing analytical formulae for the static linewidth for the vortex structure in the limit of independent vortices (i.e. moderate magnetic fields), we use Abrikosov's analysis to describe the field variations of the static linewidth at the approach of the superconductor to metal transition in the limit where the critical field is determined by Pauli depairing.

cond-mat.supr-con↗
arXiv2011

Field-Induced Spin-Exciton Condensation in dx2-y2-wave Superconducting CeCoIn5

The implications of the spin exciton mechanism are exposed in the context of a Spin Density Wave (SDW) instability occurring inside the superconducting phase of a layered heavy electron compound. In this model a magnetic field serves as a tuning parameter bringing the system to the point where the transverse spin correlations are enhanced due to dx2 -y2 -wave superconductivity and induces an instability to a phase with coexisting superconductivity and SDW order. The model considers electrons in a crystal with antiferromagnetic interactions and provides restrictions on the Fermi surface characteristics and on the ordering wave-vector (that can be commensurate or incommensurate close to commensuration). The applications of the model are addressed to the low-temperature/high-magnetic-field phase of CeCoIn5 [M. Kenzelmann et al., Science 321, 1652 (2008), Phys. Rev. Lett. 104, 127001 (2010)].

cond-mat.supr-con↗
arXiv2010

Paramagnetic Effects in the Vortex Lattice Field Distribution of Strongly Type-II Superconductors

We present an analysis of the magnetic field distribution in the Abrikosov lattice of high-$κ$ superconductors with singlet pairing in the case where the critical field is mainly determined by the Pauli limit and the superfluid currents partly come from the paramagnetic interaction of electron spins with the local magnetic field. The derivation is performed in the frame of the generalized Clem variational method which is valid not too close to the critical field and furthermore with the Abrikosov type theory in the vicinity of it. The found vortex lattice form factor increases with increasing field and then falls down at approach of the upper critical field where the superconducting state is suppressed.

cond-mat.supr-con↗
arXiv2010

Paramagnetic Effects on the Vortex Lattice of the Unconventional Superconductor CeCoIn_5

We expose an analysis of the magnetic field distribution in the Abrikosov lattice of high-kappa superconductors with d-wave pairing in the case where the critical field is mainly determined by the Pauli limit and the superfluid currents mainly come from the paramagnetic interaction of electron spins with the local magnetic field. The result found in frame of the generalized Clem variational approach is compatible with the recent observation that the form factor in CeCoIn_5 increases with increasing field and then decreases at the approach of H_c2. (A. D. Bianchi et al., Science vol. 319, 177 (2008)).

cond-mat.supr-con↗