Transport Of Quantum Information Research Articles

Breaking the mirror symmetry of photonic spin-orbit interaction using a geometrically symmetric chiral resonator

The symmetries of photonic spin-orbit interaction (PSOI) at waveguide interfaces provide flexible modulation capability but limit their practical implementation due to the stringent requirements of excitation conditions. This limitation can be mitigated by intentionally breaking local symmetries, offering a novel platform for achieving directional coupling and optical isolation with PSOI-based interfaces. For example, breaking the inversion symmetry of a nanofiber PSOI interface using a nanosphere scatterer reduces the required accuracy in the size and position of excitation spots. This study introduces a novel approach to break the mirror symmetry of a PSOI-based nanofiber waveguide by coupling it with a geometrically symmetric chiral gold nanohelicoid (GNH) resonator, which relaxes the original requirement of circularly polarized excitations. Finite-difference time-domain simulations demonstrate unidirectional light coupling and propagation under both circularly and linearly polarized excitations, showcasing the versatility of this hybrid symmetry-broken system. The Fano-like features observed in directionality spectra align with the GNH’s circular dichroism spectrum, emphasizing an intricate correlation between plasmonic near-field chirality and far-field scattering dichroism. This work paves the way for enhancing the functionalities of PSOI-based waveguide interfaces through locally coupling them with nanoscale chiral resonators, thereby expanding their application in quantum photonics, information transport and plasmonic nanophotonics.

Quantum information diode based on a magnonic crystal

Exploiting the effect of nonreciprocal magnons in a system with no inversion symmetry, we propose a concept of a quantum information diode (QID), i.e. a device rectifying the amount of quantum information transmitted in the opposite directions. We control the asymmetric left and right quantum information currents through an applied external electric field and quantify it through the left and right out-of-time-ordered correlation. To enhance the efficiency of the QID, we utilize a magnonic crystal. We excite magnons of different frequencies and let them propagate in opposite directions. Nonreciprocal magnons propagating in opposite directions have different dispersion relations. Magnons propagating in one direction match resonant conditions and scatter on gate magnons. Therefore, magnon flux in one direction is damped in the magnonic crystal leading to an asymmetric transport of quantum information in the QID. A QID can be fabricated from an yttrium iron garnet film. This is an experimentally feasible concept and implies certain conditions: low temperature and small deviation from the equilibrium to exclude effects of phonons and magnon interactions. We show that rectification of the flaw of quantum information can be controlled efficiently by an external electric field and magnetoelectric effects.

Engineering Robust Metallic Zero-Mode States in Olympicene Graphene Nanoribbons.

Metallic graphene nanoribbons (GNRs) represent a critical component in the toolbox of low-dimensional functional materials technology serving as 1D interconnects capable of both electronic and quantum information transport. The structural constraints imposed by on-surface bottom-up GNR synthesis protocols along with the limited control over orientation and sequence of asymmetric monomer building blocks during the radical step-growth polymerization have plagued the design and assembly of metallic GNRs. Here, we report the regioregular synthesis of GNRs hosting robust metallic states by embedding a symmetric zero-mode (ZM) superlattice along the backbone of a GNR. Tight-binding electronic structure models predict a strong nearest-neighbor electron hopping interaction between adjacent ZM states, resulting in a dispersive metallic band. First-principles density functional theory-local density approximation calculations confirm this prediction, and the robust, metallic ZM band of olympicene GNRs is experimentally corroborated by scanning tunneling spectroscopy.

Influence of errors on the transport of quantum information through distant quantum dot spin qubits

The ability to connect distant qubits plays a role in quantum computing and systems candidates for quantum computation must be able to interact their constituent qubits. We model the quantum dot spin qubits by a spin chain with nearest-neighbors interaction. Within this model, we interact distant qubits by consecutive SWAP gates. The SWAP gate exchanges the information of two different qubits and it is obtained by a time-dependent pulse. Also, we implement the CNOT gate, which is fundamental to universal quantum computation. These gates are applied in a system free from decoherence, which provides a fidelity with high accuracy. Furthermore, we analyze the situation where dephasing, amplitude-damping, and depolarizing types of errors occur in each site of the chain. We found that the order of the SWAP and CNOT gates is important and it can lead to a relevant difference in fidelity when the number of qubits is large.

Counterdiabatic transfer of a quantum state in a tunable Heisenberg spin chain via the variational principle

We present a couple of counterdiabatic (CD) schemes for a rapid and high-fidelity transfer of quantum state across a one-dimensional spin chain, between two weakly coupled external qubits at each end. Employing the effective low-energy Hamiltonian of the system, we first construct the optimal CD terms based on the variational principle and then put forward two experimentally feasible shortcuts, which only need to manipulate couplings between the external qubits and chain. Compared to traditional adiabatic protocol, the resulting schemes allow a drastic increase in state-transfer fidelity in a short time. Furthermore, numerical simulation demonstrates that our speed-up protocols hold robustness against the imperfections of control fields and evolution time. The proposed schemes may be applicable to fast quantum-information transport in various spin-based physical systems.

Multiple strong topological gaps and hexagonal warping in Bi4Te3

The electronic topology of ${\mathrm{Bi}}_{4}{\mathrm{Te}}_{3}$, composed of alternating ${\mathrm{Bi}}_{2}$ and ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layers, is investigated by density functional theory and angle-resolved photoemission spectroscopy. We find, remarkably, that there are three adjacent strong topological gaps with associated protected surface states within a 2-eV range of the Fermi level. The existence of three consecutive Dirac cones in $k$ space gives promise for alternative phenomena and applications, e.g., production of single photons with different energies (in the infrared and visible ranges) for multichannel transport of quantum information as well as multiple degrees of freedom in electron pumping for lasers. Additionally, a surface-state Fermi surface with strong hexagonal warping is observed.

Quantum corralling

We propose a robust and efficient way to store and transport quantum information via one-dimensional discrete time quantum walks. We show how to attain an effective dispersionless wave packet evolution using only two types of local unitary operators (quantum coins or gates), properly engineered to act at predetermined times and at specific lattice sites during the system's time evolution. In particular, we show that a qubit initially localized about a Gaussian distribution can be almost perfectly confined during long times or sent hundreds lattice sites away from its original location and later almost perfectly reconstructed using only Hadamard and ${\ensuremath{\sigma}}_{x}$ gates.

Spin shuttling in a silicon double quantum dot

The transport of quantum information between different nodes of a quantum device is among the challenging functionalities of a quantum processor. In the context of spin qubits, this requirement can be met by coherent electron spin shuttling between semiconductor quantum dots. Here we theoretically study a minimal version of spin shuttling between two quantum dots. To this end, we analyze the dynamics of an electron during a detuning sweep in a silicon double quantum dot (DQD) occupied by one electron. Possibilities and limitations of spin transport are investigated. Spin-orbit interaction and the Zeeman effect in an inhomogeneous magnetic field play an important role for spin shuttling and are included in our model. Interactions that couple the position, spin and valley degrees of freedom open a number of avoided crossings in the spectrum allowing for diabatic transitions and interfering paths. The outcomes of single and repeated spin shuttling protocols are explored by means of numerical simulations and an approximate analytical model based on the solution of the Landau--Zener problem. We find that a spin infidelity as low as $1-F_s\lesssim 0.002$ with a relatively fast level velocity of $\alpha = 600\, {\mu}$eV/ns is feasible for optimal choices of parameters or by making use of constructive interference.

Engineering topological phase transition and Aharonov–Bohm caging in a flux-staggered lattice

A tight binding network of diamond shaped unit cells trapping a staggered magnetic flux distribution is shown to exhibit a topological phase transition under a controlled variation of the flux trapped in a cell. A simple real space decimation technique maps a binary flux staggered network into an equivalent Su–Shrieffer–Heeger (SSH) model. In this way, dealing with a subspace of the full degrees of freedom, we show that a topological phase transition can be initiated by tuning the applied magnetic field that eventually simulates an engineering of the numerical values of the overlap integrals in the paradigmatic SSH model. Thus one can use an external agent, rather than monitoring the intrinsic property of a lattice to control the topological properties. This is advantageous from an experimental point of view. We also provide an in-depth description and analysis of the topologically protected edge states, and discuss how, by tuning the flux from outside one can enhance the spatial extent of the Aharonov–Bohm caging of single particle states for any arbitrary period of staggering. This feature can be useful for the study of transport of quantum information. Our results are exact.

Quantum registers hit the right wavelength.

Controlling nuclear spins coupled to an electron spin in silicon carbide has enabled development of a ‘quantum register’ interfaced with telecom photons, leading to the possibility of distant transport of quantum information.

Giant spin signals in chemically functionalized multiwall carbon nanotubes.

Transporting quantum information such as the spin information over micrometric or even millimetric distances is a strong requirement for the next-generation electronic circuits such as low-voltage spin-logic devices. This crucial step of transportation remains delicate in nontopologically protected systems because of the volatile nature of spin states. Here, a beneficial combination of different phenomena is used to approach this sought-after milestone for the beyond-Complementary Metal Oxide Semiconductor (CMOS) technology roadmap. First, a strongly spin-polarized charge current is injected using highly spin-polarized hybridized states emerging at the complex ferromagnetic metal/molecule interfaces. Second, the spin information is brought toward the conducting inner shells of a multiwall carbon nanotube used as a confined nanoguide benefiting from both weak spin-orbit and hyperfine interactions. The spin information is finally electrically converted because of a strong magnetoresistive effect. The experimental results are also supported by calculations qualitatively revealing exceptional spin transport properties of this system.

Synthesis and Magnon Thermal Transport Properties of Spin Ladder Sr14Cu24O41 Microstructures

AbstractThe spin ladder compound (Sr,Ca,La)14Cu24O41 exhibits an incommensurate layered structure with strong antiferromagnetic coupling. Besides intriguing superconducting behavior, recent experiments on bulk Sr14Cu24O41 single crystals have revealed a remarkable magnon thermal conductivity, which is the largest above 100 K among all known quantum magnets. Although bulk (Sr,Ca,La)14Cu24O41 crystals have been synthesized and studied extensively, there have been few reports on the synthesis and magnon thermal transport investigation of their microstructures. Here, the synthesis and thermal transport properties of Sr14Cu24O41 microrods are reported. Electron microscopy studies indicate that these microrods synthesized by a coprecipitation method are single crystals grown preferentially along the ladder axis. Based on a four‐probe thermal transport measurement, the thermal conductivity of the microrods reveals appreciable magnon transport in the microstructures. According to a kinetic model analysis, magnon transport in the microrods is suppressed mainly by increased point defect scattering compared to the bulk crystals, whereas surface scattering is negligible for anisotropic 1D magnon transport along the ladder. Moreover, the thermal conductivity is enhanced after annealing as a result of reduced oxygen vacancies. These results help to build the foundation for future heterogeneous integration of magnetic microstructures in microscale devices for the transport of energy and quantum information.

Two-spin entanglement induced by scattering of backscattering-free chiral electrons in a Chern insulator

The existence of robust chiral edge states in a finite topologically nontrivial chern insulator is a consequence of the bulk-boundary correspondence. In this paper, we present a theoretical framework based on lattice Green's function to study the scattering of such chiral edge electrons by a single localized impurity. To this end, in the first step, we consider the standard topological Haldane model on a honeycomb lattice with strip geometry. We obtain analytical expressions for the wave functions and their corresponding energy dispersion of the low-energy chiral states localized at the edge of the ribbon. Then, we employ the $T$-matrix Lippmann-Schwinger approach to explicitly show the robustness of chiral edge states against the impurity scattering. This backscattering-free process has an interesting property that the transmitted wave function acquires an additional phase factor. Although this additional phase factor does not affect quantum transport through the chiral channel it can carry quantum information. As an example of such quantum information transport, we investigate the entanglement of two magnetic impurities in a chern insulator through the dissipation-less scattering of chiral electrons.

Engineering fragile topology in photonic crystals: Topological quantum chemistry of light

In recent years, there have been rapid advances in the parallel fields of electronic and photonic topological crystals. Topological photonic crystals in particular show promise for coherent transport of light and quantum information at macroscopic scales. In this work, we apply for the first time the recently developed theory of "Topological quantum chemistry" to the study of band structures in photonic crystals. This method allows us to design and diagnose topological photonic band structures using only group theory and linear algebra. As an example, we focus on a family of crystals formed by elliptical rods in a triangular lattice. We show that the symmetry of Bloch states in the Brillouin zone can determine the position of the localized photonic wave packets describing groups of bands. By modifying the crystal structure and inverting bands, we show how the centers of these wave packets can be moved between different positions in the unit cell. Finally, we show that for shapes of dielectric rods, there exist isolated topological bands which do not admit a well-localized description, representing the first physical instance of "fragile" topology in a truly noninteracting system. Our work demonstrates how photonic crystals are the natural platform for the future experimental investigation of fragile topological bands.

Telecom photon interface of solid-state quantum nodes

Solid-state spins such as nitrogen-vacancy (NV) center are promising platforms for large-scale quantum networks. Despite the optical interface of NV center system, however, the significant attenuation of its zero-phonon-line photon in optical fiber prevents the network extended to long distances. Therefore a telecom-wavelength photon interface would be essential to reduce the photon loss in transporting quantum information. Here we propose an efficient scheme for coupling telecom photon to NV center ensembles mediated by rare-earth doped crystal. Specifically, we proposed protocols for high fidelity quantum state transfer and entanglement generation with parameters within reach of current technologies. Such an interface would bring new insights into future implementations of long-range quantum network with NV centers in diamond acting as quantum nodes.

Adiabatic state distribution using anti-ferromagnetic spin systems

Transporting quantum information is an important prerequisite for quantum computers. We study how this can be done in Heisenberg-coupled spin networks using adiabatic control over the coupling strengths. We find that qudits can be transferred and entangled pairs can be created between distant sites of bipartite graphs with a certain balance between the maximum spin of both parts, extending previous results that were limited to linear chains. The transfer fidelity in a small star-shaped network is numerically analysed, and possible experimental implementations are discussed.

Unveiling noiseless clusters in complex quantum networks

The transport and storage of quantum information, excitations, and entanglement, within and across complex quantum networks is crucially affected by the presence of noise induced by their surroundings. Generally, the interaction with the environment deteriorates quantum properties initially present, thus limiting the efficiency of any quantum-enhanced protocol or phenomenon. This is of key relevance, for example, in the design of quantum communication networks and for understanding and controlling quantum harvesting on complex systems. Here, we show that complex quantum networks, such as random and small-world ones, can admit noiseless clusters for collective dissipation. We characterize these noiseless structures in connection to their topology addressing their abundance, extension, and configuration, as well as their robustness to noise and experimental imperfections. We show that the network degree variance controls the probability to find noiseless modes and that these are mostly spanning an even number of nodes, like breathers. For imperfections across the network, a family of quasi-noiseless modes is also identified shielded by noise up to times decreasing linearly with frequency inhomogeneities. Large noiseless components are shown to be more resilient to the presence of detuning than to differences in their coupling strengths. Finally, we investigate the emergence of both stationary and transient quantum synchronization showing that this is a rather resilient phenomenon in these networks.

Transport of spatial squeezing through an optical waveguide.

Multi-core optical fibers are readily used in endoscopic devices to transmit classical images. As an extension to the quantum domain, we study the transmission of the spatial quantum fluctuations of light through a conduit made of the ordered packing of thousands of fibers. Starting from twin beams that are correlated in their local intensity fluctuations, we show that, in the limit of a high density of constituent fiber cores, the intensity-difference squeezing present in arbitrary matching regions of the beams is preserved when one of the beams is sent through the conduit. The capability of using fiber bundles to transport quantum information encoded in the spatial degrees of freedom could bring guided-light technology to the emergent field of quantum imaging.

Detecting Equilibrium and Dynamical Quantum Phase Transitions in Ising Chains via Out-of-Time-Ordered Correlators.

Out-of-time-ordered (OTO) correlators have developed into a central concept quantifying quantum information transport, information scrambling, and quantum chaos. In this Letter, we show that such an OTO correlator can also be used to dynamically detect equilibrium as well as nonequilibrium phase transitions in Ising chains. We study OTO correlators of an order parameter both in equilibrium and after a quantum quench for different variants of transverse-field Ising models in one dimension, including the integrable one as well as nonintegrable and long-range extensions. We find for all the studied models that the OTO correlator in ground states detects the quantum phase transition. After a quantum quench from a fully polarized state, we observe numerically for the short-range models that the asymptotic long-time value of the OTO correlator signals still the equilibrium critical points and ordered phases. For the long-range extension, the OTO correlator instead determines a dynamical quantum phase transition in the model. We discuss how our findings can be observed in current experiments of trapped ions or Rydberg atoms.

Brillouin cooling in a linear waveguide

Brillouin scattering is not usually considered as a mechanism that can cause cooling of a material due to the thermodynamic dominance of Stokes scattering in most practical systems. However, it has been shown in experiments on resonators that net phonon annihilation through anti-Stokes Brillouin scattering can be enabled by means of a suitable set of optical and acoustic states. The cooling of traveling phonons in a linear waveguide, on the other hand, could lead to the exciting future prospect of manipulating unidirectional phonon fluxes and even the nonreciprocal transport of quantum information via phonons. In this work, we present an analysis of the conditions under which Brillouin cooling of phonons of both low and high group velocities may be achieved in a linear waveguide. We analyze the three-wave mixing interaction between the optical and traveling acoustic modes that participate in forward Brillouin scattering, and reveal the key regimes of operation for the process. Our calculations indicate that measurable cooling may occur in a system having phonons with spatial loss rate that is of the same order as the spatial optical loss rate. If the Brillouin gain in such a waveguide reaches the order of 105 m−1 W−1, appreciable cooling of phonon modes may be observed with modest pump power of a few mW.