62 research outputs found
Superlattice platform for chiral superconductivity with tuneable and high Chern numbers
Finding concrete realizations for topologically nontrivial chiral
superconductivity has been a long-standing goal in quantum matter research.
Here we propose a route to a systematic realization of chiral superconductivity
with nonzero Chern numbers. This goal can be achieved in a nanomagnet lattice
deposited on top of a spin-orbit coupled two-dimensional electron gas (2DEG)
with proximity s-wave superconductivity. The proposed structure can be regarded
as a universal platform for chiral superconductivity supporting a large variety
of topological phases. The topological state of the system can be electrically
controlled by, for example, tuning the density of the 2DEG.Comment: 5+6 pages, 4 figure
Topological superconductivity in ferromagnetic atom chains beyond the deep-impurity regime
Recent developments in the search for topological superconductivity have
brought lattices of magnetic adatoms on a superconductor into intense focus. In
this work we will study ferromagnetic chains of adatoms on superconducting
surfaces with Rashba spin-orbit coupling. Generalising the deep-impurity
approach employed extensively in previous works to arbitrary subgap energies,
we formulate the theory of the subgap spectrum as a nonlinear matrix eigenvalue
problem. We obtain an essentially analytical description of the subgap
spectrum, allowing an efficient study of the topological properties. Employing
a flat-band Hamiltonian sharing the topological properties of the chain, we
evaluate the -valued winding number and discover five distinct
topological phases. Our results also confirm that the topological band
formation does not require the decoupled Shiba energies to be fine-tuned to the
gap centre. We also study the properties of Majorana bound states in the
system.Comment: 11 pages, 16 figure
Majorana states in helical Shiba chains and ladders
Motivated by recent proposals to realize Majorana bound states in chains and
arrays of magnetic atoms deposited on top of a superconductor, we study the
topological properties of various chain structures, ladders and two-dimensional
arrangements exhibiting magnetic helices. We show that magnetic domain walls
where the chirality of a magnetic helix is inverted support two protected
Majorana states giving rise to a tunneling conductance peak twice the height of
a single Majorana state. The topological properties of coupled chains exhibit
nontrivial behaviour as a function of the number of chains beyond the even-odd
dichotomy expected from the simple nature of coupled Majorana
states. In addition, it is possible that a ladder of two or more coupled chains
exhibit Majorana edge states even when decoupled chains are trivial. We
formulate a general criterion for the number of Majorana edge states in
multichain ladders and discuss some experimental consequences of our findings.Comment: 6 pages, 7 Fig
Amorphous topological superconductivity in a Shiba glass
Topological states of matter support quantized nondissipative responses and
exotic quantum particles that cannot be accessed in common materials. The
exceptional properties and application potential of topological materials have
triggered a large-scale search for new realizations. Breaking away from the
popular trend focusing almost exclusively on crystalline symmetries, we
introduce the Shiba glass as a platform for amorphous topological quantum
matter. This system consists of an ensemble of randomly distributed magnetic
atoms on a superconducting surface. The collection of magnetic moments gives
rise to subgap Yu-Shiba-Rusinov states that form a topological superconducting
phase at critical density despite a complete absence of spatial order.
Experimental signatures of the amorphous topological state can be obtained by
STM measurements probing the topological edge mode. Our discovery demonstrates
the physical feasibility of amorphous topological quantum matter and presents a
concrete route to fabricating new topological systems from nontopological
materials with random dopants.Comment: 11 pages, 5 figure
Entanglement echo and dynamical entanglement transitions
We formulate dynamical phase transitions in subsystems embedded in larger quantum systems. Introducing the entanglement echo as an overlap of the initial and instantaneous entanglement ground states, we show its analytic structure after a quench provides natural definition of dynamical phase transitions in the subsystem. These transitions come in two varieties: the entanglement-type transitions and the bulk-type Loschmidt transitions. The entanglement-type transitions arise from periodic reorganization of quantum correlations between the subsystem and its environment, manifesting in instantaneous entanglement ground state degeneracies. Furthermore, the entanglement echo distinguishes the direction of the quench, resolves spatially distinct dynamical phase transitions for nonuniform quenches, and give rise to sharply defined transitions for mixed initial states. We propose an experimental probe to identify entanglement-type transitions through temporal changes in subsystem fluctuations.Non peer reviewe
Topological properties of helical Shiba chains with general impurity strength and hybridization
Recent experiments announced an observation of topological superconductivity
and Majorana quasiparticles in Shiba chains, consisting of an array of magnetic
atoms deposited on top of a superconductor. In this work we study helical Shiba
chains and generalize the microscopic theory of subgap energy bands to a regime
where the decoupled magnetic impurity energy and the hybridization of different
impurity states can be significant compared to the superconducting gap of the
host material. From exact solutions of the Bogoliubov-de Gennes equation we
extract expressions for the topological phase boundaries for arbitrary values
of the superconducting coherence length. The subgap spectral problem can be
formulated as a nonlinear matrix eigenvalue problem from which we obtain an
analytical solution for energy bands in the long coherence length limit.
Physical consequences and departures from the previously obtained results in
the deep-dilute impurity limit are discussed in detail.Comment: 10 pages, 8 figure
Engineering of Chern insulators and circuits of topological edge states
Impurities embedded in electronic systems induce bound states which under
certain circumstances can hybridize and lead to impurity bands. Doping of
insulators with impurities has been identified as a promising route towards
engineering electronic topological states of matter. In this paper we show how
to realize tuneable Chern insulators starting from a three dimensional
topological insulator whose surface is gapped and intentionally doped with
magnetic impurities. The main advantage of the protocol is that it is robust,
and in particular not very sensitive to the impurity configuration. We
explicitly demonstrate this for a square lattice of impurities as well as a
random lattice. In both cases we show that it is possible to change the Chern
number of the system by one through manipulating its topological state. We also
discuss how this can be used to engineer circuits of edge channels.Comment: 9 pages, 6 figure
Many-body entanglement and topology from uncertainties and measurement-induced modes
We present universal characteristics of quantum entanglement and topology through virtual entanglement modes that fluctuate into existence in subsystem measurements. For generic interacting systems and extensive conserved quantities, these modes give rise to a statistical uncertainty which corresponds to entanglement entropies. Consequently, the measurement-induced modes provide directly observable route to entanglement and its scaling laws. Moreover, in topological systems, the measurement-induced edge modes give rise to quantized and nonanalytic uncertainties, providing easily accessible signatures of topology. Our work provides a much-needed direct method to probe the performance of emerging quantum simulators to realize entangled and topological states.Peer reviewe
Boiling Quantum Vacuum : Thermal Subsystems from Ground-State Entanglement
In certain special circumstances, such as in the vicinity of a black hole or in a uniformly accelerating frame, vacuum fluctuations appear to give rise to a finite-temperature environment. This effect, currently without experimental confirmation, can be interpreted as a manifestation of quantum entanglement after tracing out vacuum modes in an unobserved region. In this work, we identify a class of experimentally accessible quantum systems where thermal density matrices emerge from vacuum entanglement. We show that reduced density matrices of lower-dimensional subsystems embedded in D-dimensional gapped Dirac fermion vacuum, either on a lattice or continuum, have a thermal form with respect to a lower-dimensional Dirac Hamiltonian. Strikingly, we show that vacuum entanglement can even conspire to make a subsystem of a gapped system at zero temperature appear as a hot gapless system. We propose concrete experiments in cold-atom quantum simulators to observe the vacuum-entanglement-induced thermal states.Peer reviewe
Exponential shortcut to measurement-induced entanglement phase transitions
Recently discovered measurement-induced entanglement phase transitions in
monitored quantum circuits provide a novel example of far-from-equilibrium
quantum criticality. Here, we propose a highly efficient strategy for
experimentally accessing these transitions through fluctuations. Instead of
directly measuring entanglement entropy, which requires an exponential number
of measurements in the subsystem size, our method provides a scalable approach
to entanglement transitions in the presence of conserved quantities. In analogy
to entanglement entropy and mutual information, we illustrate how bipartite and
multipartite fluctuations can both be employed to analyze the
measurement-induced criticality. Remarkably, the phase transition can be
revealed by measuring fluctuations of only a handful of qubits.Comment: 6 pages, 4 figure
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