Quantum Information Transfer Research Articles

Generation, characterization, and manipulation of quantum correlations in electron beams

Entanglement engineering plays a central role in quantum-enhanced technologies, with potential physical platforms that outperform their classical counterparts. However, free electrons remain largely unexplored despite their great capacity to encode and manipulate quantum information, due in part to the lack of a suitable theoretical framework. Here we link theoretical concepts from quantum information to available free-electron sources. Specifically, we consider the interactions among electrons propagating near the surface of a polariton-supporting medium and study the entanglement induced by pair-wise coupling. These correlations depend on the controlled interaction interval and the initial electron bandwidth. We show that long interaction times of broadband electrons extend their temporal coherence. This in turn is revealed through a widened Hong–Ou–Mandel peak and is associated with an increased entanglement entropy. We then introduce a discrete basis of electronic temporal modes and discriminate between them via coincidence detection with a shaped probe. This paves the way for ultrafast quantum information transfer by means of free electrons, rendering the large alphabet that they span in the time domain accessible.

Frequency-multiplexed hybrid optical entangled source based on the Pockels effect

In the recent years important experimental advances in resonant electro-optic modulators as high-efficiency sources for coherent frequency combs and as devices for quantum information transfer have been realized, where strong optical and microwave mode coupling were achieved. These features suggest electro-optic-based devices as candidates for entangled optical frequency comb sources. In the present work, I study the generation of entangled optical frequency combs in millimeter-sized resonant electro-optic modulators. These devices profit from the experimentally proven advantages such as nearly constant optical free spectral ranges over several gigahertz, and high optical and microwave quality factors. The generation of frequency multiplexed quantum channels with spectral bandwidth in the MHz range for conservative parameter values paves the way towards novel uses in long-distance hybrid quantum networks, quantum key distribution, enhanced optical metrology, and quantum computing.

Influence of Water Polarization Caused by Phonon Resonance on Catalytic Activity of Enolase.

Enolase is a conservative protein. Its cellular enzymatic activity catalyzes the conversion of 2-phospho-d-glycerate (2-PGA) to a phosphoenolpyruvate (PEP) product in the glycolysis pathway. This enzyme also has a multifunctional nature participating in several biological processes. This work aims to determine the effect of water polarization on the catalytic activity of enolase. The experiments have been set based on the concept that water, a polar dielectric, may undergo the phenomenon of electric polarization, decreasing its configurational and vibrational entropy. Prior to the reaction, the 2-PGA substrate was incubated for 5 h in the glass cuvette with an attached chip-inductor. The latter device was designed to transfer quantum information about a given quantum state from the quantum state generator to water by a phonon resonance. Then, such substrate samples preincubated with the chip-inductor were removed every hour in a separate quartz cuvette with the enzyme to determine its catalytic activity. The influence of the chip-inductor on the preincubated substrate resulted in an increase in the catalytic activity of enolase by 30% compared to the control substrate, not preincubated with the chip-inductor. This suggests that the catalytic activity of the enzyme is augmented when the substrate was primed by chip-inductors. In another kind of experiment, wherein enolase was exposed to methylglyoxal modification, the catalytic activity of the enzyme dropped to 71.7%, while the same enzyme glycated with methylglyoxal primed by chip-inductors restored its activity by 8.4%. This shows the protective effect of chip-inductors on enolase activity despite the harmful effect of methylglyoxal on the protein.

Effective inhibit energetic cost in stimulated Raman shortcut-to-adiabatic passage

A shortcut to the adiabatic process is an effective method for quantum information processing. The fast and robust quantum information transfer can be implemented by this method. The energetic cost is an important measurement for the shortcut. In this paper, we investigate how to inhibit the energetic cost in stimulated Raman shortcut-to-adiabatic passage in a three-level system. The energetic cost can be manipulated by adjusting detuning of the system and the energetic cost takes the minimum with one-photon resonance condition.

Research on controlling the perfect transfer of the two-qubit quantum information in spin chain

Perfect transfer of the two-qubit quantum information in spin chain without any magnetic field is investigated. In our work, the spin chain is placed in a particular low-intensity magnetic field whose value is symmetrical about the chain and whose difference value between the nearest lattice points is constant. And the influence of the magnetic field has been studied by the method of matrix diagonalization. It is shown that the difference value of the magnetic field determines the fidelity of the two-qubit quantum information transfer in the spin chain. On the basis of this, we propose a theoretical scheme to achieve the quantum control of the two-qubit quantum information perfect transfer by applying this magnetic field, so that the perfect transfer time of information can be controlled arbitrarily as needed.

Quantum Coherence and Transfer of Quantum Information with a Kerr Medium Under Decoherence

We investigate the dynamics of quantum coherence of a system consisting of two interacting atoms coupling with a common cavity which is filled with a nonlinear Kerr-like medium, in the presence of intrinsic decoherence. It is shown that the stationary quantum coherence can arise in the system as the time approach to infinite. In particular, the amount of stationary quantum coherence can be enhanced by adjusting the Kerr interaction and dipole-dipole interaction. Furthermore, we also explore the influence of Kerr interaction and dipole-dipole interaction on the transfer of quantum information by a witness of the trace distance and find that the transferred information and stationary quantum information can be controlled by the Kerr interaction and dipole-dipole interaction.

Generation of Schrödinger-cat states through photon-assisted Landau-Zener-Stückelberg interferometry

Schr\"odinger cat states are useful for many applications, ranging from quantum information processing to high-precision measurements. In this paper we propose a conceptually new method for creating such cat states, based on photon-assisted Landau-Zener-St\"uckelberg interferometry in a hybrid system consisting of a qubit coupled to a photon cavity. We show that by initializing the qubit in one of its basis states, performing three consecutive sweeps of the qubit energy splitting across the 1-photon resonance, and finally projecting the qubit to the same basis state, the parity of the photon field can be purified to very high degree; when the initial photon state is a coherent state, the final state will then be very close to a Schr\"odinger cat state. We present numerical simulations that confirm that our protocol could work with high fidelity ($\sim 0.99$) for coherent states of reasonable size ($|\alpha|^2 \sim 10$). Furthermore, we suggest that our protocol can also be used to transfer quantum information between the qubit and a superposition of orthogonal cat states in the cavity.

Quantum control of quantum information perfect transfer in arbitrary-length spin chain

The single-bit quantum information perfect transfer determined only by the dynamic evolution of the system in a spin chain is investigated. Our results show that the quantum control of the above quantum information perfect transfer can be achieved by applying a low-intensity symmetric magnetic field to the spin chain. We have studied the influence of the magnetic field on the perfect transfer of quantum information in the arbitrary-length spin chain. It gives that the time of the quantum information perfect transfer is determined by applying the low-intensity magnetic field which is symmetric about the spin chain and whose difference value is constant between the closed lattices in the spin chain. Furthermore, we put forward a scheme to achieve the quantum control of quantum information perfect transfer in the arbitrarily-length spin chain by applying the magnetic field.

High‐Speed Quantum Transducer with a Single‐Photon Emitter in a 2D Resonator

AbstractQuantum transducers can transfer quantum information between different systems. Microwave–optical photon conversion is important for future quantum networks to interconnect remote superconducting quantum computers with optical fibers. Here, a high‐speed quantum transducer based on a single‐photon emitter in an atomically thin membrane resonator, that can couple single microwave photons to single optical photons, is proposed. The 2D resonator is a freestanding van der Waals heterostructure (which may consist of hexagonal boron nitride, graphene, or other 2D materials) that hosts a quantum emitter. The mechanical vibration (phonon) of the 2D resonator interacts with optical photons by shifting the optical transition frequency of the single‐photon emitter with strain or the Stark effect. The mechanical vibration couples to microwave photons by shifting the resonant frequency of an LC circuit that includes the membrane. Thanks to the small mass of the 2D resonator, both the single‐photon optomechanical coupling strength and the electromechanical coupling strength can reach the strong coupling regime. This provides a way for high‐speed quantum state transfer between a microwave photon, a phonon, and an optical photon.

Unscrambling entanglement through a complex medium

The transfer of quantum information through a noisy environment is a central challenge in the fields of quantum communication, imaging and nanophotonics. In particular, high-dimensional quantum states of light enable quantum networks with significantly higher information capacities and noise robustness as compared with qubits. However, although qubit entanglement has been distributed over large distances through free space and fibre, the transport of high-dimensional entanglement is hindered by the complexity of the channel, which encompasses effects such as free-space turbulence or mode mixing in multimode waveguides. Here, we demonstrate the transport of six-dimensional spatial-mode entanglement through a 2-m-long, commercial multimode fibre with 84.4% fidelity. We show how the entanglement can itself be used to measure the transmission matrix of the complex medium, allowing the recovery of quantum correlations that were initially lost. Using a unique property of entangled states, the medium is rendered transparent to entanglement by carefully 'scrambling' the photon that did not enter it, rather than unscrambling the photon that did. Our work overcomes a primary challenge in the fields of quantum communication and imaging, and opens a new pathway towards the control of complex scattering processes in the quantum regime.

Coherent Multispin Exchange Coupling in a Quantum-Dot Spin Chain

Heisenberg exchange coupling between neighboring electron spins in semiconductor quantum dots provides a powerful tool for quantum information processing and simulation. Although so far unrealized, extended Heisenberg spin chains can enable long-distance quantum information transfer and the generation of non-equilibrium quantum states. In this work, we implement simultaneous, coherent exchange coupling between all nearest-neighbor pairs of spins in a quadruple quantum dot. The main challenge in implementing simultaneous exchange couplings is the nonlinear and nonlocal dependence of the exchange couplings on gate voltages. Through a combination of electrostatic simulation and theoretical modeling, we show that this challenge arises primarily due to lateral shifts of the quantum dots during gate pulses. Building on this insight, we develop two models, which can be used to predict the confinement gate voltages for a desired set of exchange couplings. Although the model parameters depend on the number of exchange couplings desired (suggesting that effects in addition to lateral wavefunction shifts are important), the models are sufficient to enable simultaneous and independent control of all three exchange couplings in a quadruple quantum dot. We demonstrate two-, three-, and four-spin exchange oscillations, and our data agree with simulations.

Quantum information transfer and entangled state generation using superconducting qubits in the absence and presence of dissipation

In this paper, we propose a scheme for quantum information transfer by a gap-tunable bridge qubit between two superconducting (SC) qubits, which are initially prepared in separable quantum states. As is observed, enough high-fidelity and maximally entanglement between the two superconducting resonators, as well as between the two of qubits, can be achieved. It is shown that by implementing driven magnetic field to high detuned superconducting qubits, we are able to induce sidebands in the qubit–resonator and also qubit–qubit couplings. The influence of decay rates of qubits and resonator modes on the dynamics of quantum fidelity and entanglement is also investigated, either individually or simultaneously, by numerical analysis. Our numerical results show that the decay rate parameters have destructive, constructive, and no critical effect on the fidelity, depending on the chosen decay parameters. Moreover, they have destructive effects on the generated entangled state in the outlined quantum information transfer process.

Conditional teleportation of quantum-dot spin states

Among the different platforms for quantum information processing, individual electron spins in semiconductor quantum dots stand out for their long coherence times and potential for scalable fabrication. The past years have witnessed substantial progress in the capabilities of spin qubits. However, coupling between distant electron spins, which is required for quantum error correction, presents a challenge, and this goal remains the focus of intense research. Quantum teleportation is a canonical method to transmit qubit states, but it has not been implemented in quantum-dot spin qubits. Here, we present evidence for quantum teleportation of electron spin qubits in semiconductor quantum dots. Although we have not performed quantum state tomography to definitively assess the teleportation fidelity, our data are consistent with conditional teleportation of spin eigenstates, entanglement swapping, and gate teleportation. Such evidence for all-matter spin-state teleportation underscores the capabilities of exchange-coupled spin qubits for quantum-information transfer.

Noisy Quantum State Redistribution With Promise and the Alpha-Bit

We consider a variation of the well-studied quantum state redistribution task, in which the starting state is known only to the receiver Bob and not to the sender Alice. We refer to this as quantum state redistribution with a one-sided promise. In addition, we consider communication from Alice to Bob over a noisy channel $\mathcal{N}$, instead of the noiseless channel, as is usually considered in state redistribution. We take a natural approach towards the solution of this problem where we "embed" the promise as part of the state and then invoke known protocols for quantum state redistribution composed with known protocols for transfer of quantum information over noisy channels. Using our approach, we are able to reproduce the Alpha-bit capacities with or without entanglement assistance in Ref. [ArXiv:1706.09434], using known protocols for quantum state redistribution and quantum communication over noisy channels. Furthermore, we generalize the entanglement assisted classical Alpha-bit capacity, showing that any quantum state redistribution protocol can be used as a black box to simulate classical communication.

Single-photon quantum router based on asymmetric intercavity couplings

As a special quantum node in a quantum network, the quantum router plays an important role in storing and transferring quantum information. In this paper, we propose a quantum router scheme based on asymmetric intercavity couplings and a three-level Λ-type atomic system. This scheme implements the quantum routing capability very well. It can perfectly transfer quantum information from one quantum channel to another. Compared with the previous quantum routing scheme, our proposed scheme can achieve the transfer rate of single photons from one quantum channel to another quantum channel reaching 100%, the high transfer rate is located in the almost quadrant regions with negative values of the two variables λa and λb, and their maximum values emerge in the center point λa = λb = −1. Therefore, it is possibly feasible to efficiently enhance the routing capability of the single photons between two channels by adjusting the inter-resonator couplings, and the asymmetric intercavity coupling provides a new method for achieving high-fidelity quantum routers.

Collectively Enhanced Chiral Photon Emission from an Atomic Array near a Nanofiber.

Emitter ensembles interact collectively with the radiation field. In the case of a one-dimensional array of atoms near a nanofiber, this collective light-matter interaction does not only lead to an increased photon coupling to the guided modes within the fiber, but also to a drastic enhancement of the chirality in the photon emission. We show that near-perfect chirality can be achieved already for moderately sized ensembles, containing 10 to 15 atoms, by phase matching a superradiant collective guided emission mode via an external laser field. This is of importance for developing an efficient interface between atoms and waveguide structures with unidirectional coupling, with applications in quantum computing and communication such as the development of nonreciprocal photon devices or quantum information transfer channels.

Simulation of topological phases with color center arrays in phononic crystals

We propose an efficient scheme for simulating the topological phases of matter based on silicon-vacancy (SiV) center arrays in phononic crystals. This phononic band gap structure allows for long-range spin-spin interactions with a tunable profile. Under a particular periodic microwave driving, the band-gap mediated spin-spin interaction can be further designed with the form of the Su-Schrieffer-Heeger (SSH) Hamiltonian. In momentum space, we investigate the topological characters of the SSH model, and show that the topological nontrivial phase can be obtained through modulating the periodic driving fields. Furthermore, we explore the zero-energy topological edge states at the boundary of the color center arrays, and study the robust quantum information transfer via the topological edge states. This setup provides a scalable and promising platform for studying topological quantum physics and quantum information processing with color centers and phononic crystals.

One-step transfer of quantum information for a photonic cat-state qubit

We present a way to transfer quantum information of a photonic cat-state qubit (cqubit) between two cavities coupled to an artificial atom. The two logic states of the photonic cqubit here are encoded by two orthogonal cat states (i.e. superpositions of coherent states) of photons. We show that quantum information of one photonic cqubit can be deterministically transferred between two cavities, with a single-step operation only. As a specific example, we numerically analyse the experimental implementation of this proposal, by considering a set-up of two microwave cavities coupled to a superconducting artificial atom. This proposal can also be applied to transfer one-cqubit quantum information between two modes of a quantum field coupled by a natural or artificial atom.

Matrix elements of the dipole-dipole interaction between two two-level atoms distanced arbitrarily from each other

Purpose. As a standard model for describing the processes of a resonant transmission of quantum information on arbitrary distances is the system of two identical two-level atoms, one of which is under radiation of the field of real photons. Such a system can serve as a basis for the construction of an element basis of quantum computers. The purpose of this paper is to study the different modes of dynamics of a system of two identical two-level atoms when they interacts with the field of real photons. Methods. In this paper, we propose a general approach to the description of the processes for the transfer of quantum information from one atom-qubit to another on the arbitrary interatomic distances, which includes two types of new physical effects: the attenuation of quantum states and the retardation of the dipole-dipole interaction. Results. The optical properties of a system of two identical two-level atoms in collective (symmetric Ψ s and antisymmetric Ψ a ) Bell states at arbitrary interatomic distances are investigated. The closed analytical expressions for the shifts and widths of the considered collective states are considered, taking into account the retarded dipole-dipole interaction of atoms. In calculation of the radial matrix elements of the dipole-dipole interaction, the wave functions of the model Fues potential are used. Conclusions. A detailed study of the mechanisms of resonant transmission of the excitation energy at arbitrary distances between the two-element atoms has an important practical significance for the physical realization of the logical operator CNOT.

Reflexivity, coding and quantum biology

Biological systems are fundamentally computational in that they process information in an apparently purposeful fashion rather than just transferring bits of it in a purely syntactical manner. Biological information, such has genetic information stored in DNA sequences, has semantic content. It carries meaning that is defined by the molecular context of its cellular environment. Information processing in biological systems displays an inherent reflexivity, a tendency for the computational information-processing to be “about” the behaviour of the molecules that participate in the computational process. This is most evident in the operation of the genetic code, where the specificity of the reactions catalysed by the aminoacyl-tRNA synthetase (aaRS) enzymes is required to be self-sustaining. A cell’s suite of aaRS enzymes completes a reflexively autocatalytic set of molecular components capable of making themselves through the operation of the code. This set requires the existence of a body of reflexive information to be stored in an organism’s genome. The genetic code is a reflexively self-organised mapping of the chemical properties of amino acid sidechains onto codon “tokens”. It is a highly evolved symbolic system of chemical self-description. Although molecular biological coding is generally portrayed in terms of classical bit-transfer events, various biochemical events explicitly require quantum coherence for their occurrence. Whether the implicit transfer of quantum information, qbits, is indicative of wide-ranging quantum computation in living systems is currently the subject of extensive investigation and speculation in the field of Quantum Biology.