Achieving robust and scalable remote quantum entanglement is one of the fundamental challenges for the development of distributed quantum networks and modular quantum computing systems. In this context, perfect state transfer (PST) and fractional state transfer (FST) have emerged as promising schemes for quantum state transfer and remote entanglement generation using only nearest-neighbor couplings. In this work, we propose a quantum state transfer scheme based on a zig-zag configuration, which introduces a control parameter for PST and FST. We show that this new parameter can suppress the population in the intermediate qubits, thereby reducing losses and enhancing state transfer. In certain limiting cases, our new scheme reduces to the conventional PST scheme, revealing an elegant mathematical structure inherent in the design. We experimentally demonstrate our proposed scheme on a superconducting quantum processor, achieving an 18% reduction in error for remote Bell state generation in a 1D ( 1 × 5 ) qubit chain with enhanced robustness to specific noise channels. Furthermore, we extend our approach to a 2D ( 3 × 3 ) network and successfully generate a W state among the four corner qubits. These results highlight the potential of our new enhanced quantum state transfer scheme for scalable and noise-resilient quantum communication and computing.

Quantum entanglement is a key feature of quantum mechanics. It describes connections between quantum systems that classical theories cannot explain. The idea of entanglement started with the Einstein–Podolsky–Rosen (EPR) argument. This argument questioned whether quantum theory was complete and showed the non-classical nature of quantum correlations. Schrödinger later defined the concept and introduced the term "entanglement" to describe composite quantum states that cannot be separated. Bell then created a framework that showed the predictions of quantum mechanics clash with local hidden-variable theories, leading to Bell’s inequality. Experiments by Aspect and others provided strong evidence for the violation of Bell’s inequalities and supported the reality of entanglement. Building on these theories and experiments, quantum teleportation became an important protocol in quantum information science. Bennett and his team proposed a scheme that showed how an unknown quantum state can be sent between distant parties using shared entanglement and classical communication, without sending the quantum system itself. Later experiments confirmed that this protocol works across different physical platforms. This paper reviews the historical development of quantum entanglement and its role in the emergence of quantum teleportation. In addition to the theoretical discussion, the teleportation protocol is implemented using IBM’s Qiskit framework. The simulation results demonstrate the successful transfer of quantum states within the circuit model, illustrating how fundamental quantum communication concepts can be explored using quantum computing simulation tools.

Thermal noise-immunized quantum state transfer through a microwave waveguide

Abstract The transport of quantum states is a crucial aspect of information processing systems, facilitating operations such as quantum key distribution and inter-component communication within quantum computers. Most quantum networks rely on symmetries to achieve an efficient state transfer. A straightforward way to design such networks is to use spatial symmetries, which severely limits the design space. Our work takes a novel approach to designing photonic networks that do not exhibit any conventional spatial symmetries, yet nevertheless support an efficient transfer of quantum states. Paradoxically, while a perfect transfer efficiency is technically unattainable in these networks, a fidelity arbitrarily close to unity is always reached within a finite time of evolution. Key to this approach are so-called latent, or 'hidden', symmetries, which are embodied in the spectral properties of the network. Latent symmetries substantially expand the design space of quantum networks and hold significant potential for applications in quantum cryptography and secure state transfer. We experimentally realize such a nine-site latent-symmetric network and successfully observe state transfer between two sites with a measured fidelity of 75%. Furthermore, by launching a two-photon state, we show that quantum interference is preserved by the network. This demonstrates that the latent symmetries enable efficient quantum state transfer, while offering greater flexibility in designing quantum networks.

Traditional many-body teleportation relies on the strong interaction property of a quantum many-body system, which usually requires numerous qubits and entanglement resources, making it difficult to realize experimentally. A natural scheme is to use a 1D spin chain with simple structure to realize many-body teleportation. In this paper, we analyze the conditions for general quantum many-body teleportation and construct an effective control Hamiltonian, realizing quantum many-body teleportation on the controlled 1D spin chain. Our scheme, which only requires forward evolution and local measurements, can be used to perform quantum state transfer without the special presetting and modulation of coupling parameters of the chain and without strict control over the evolution time, thereby enhancing the experimental realizability. Furthermore, we improve the efficiency and accuracy of quantum state transfer by introducing quantum optimal control (QOC) technique to optimize the control pulse sequences.

Quantum teleportation enables the secure transfer of unknown quantum states between remote users and is a key technology in quantum information science. Networks based on continuous-variable entangled states can extend both the user capacity and the transmission distance of quantum teleportation. This paper analyzes quantum teleportation network schemes based on three types of continuous-variable entangled states (EPR entangled state, GHZ entangled state, and linear cluster entangled state). The results show that due to the correlation properties of different types of entangled states, different quantum teleportation networks have advantages in terms of fidelity, transmission distance, and quantum resource consumption of quantum teleportation. For low-error-rate applications such as quantum computing, EPR states provide the highest fidelity. When parallel teleportation of multiple states is required, networks based on EPR or cluster entangled states provide the necessary throughput performance. In scenarios where quantum resources are severely limited, the GHZ-based teleportation protocols minimize the number of entangled modes while preserving acceptable fidelity. For applications demanding controlled teleportation, both GHZ and cluster states supply the essential multi-party correlations. Notably, cluster states offer a practical trade-off between fidelity and resource overhead, rendering them attractive for certain implementations. This study provides a reference for the design of multi-user metropolitan quantum teleportation networks.

Absorption and emission, fundamental interactions between light and matter, enable the regeneration of a quantum state of light via matter through concatenated quantum state transfer based on the principle of quantum teleportation. This transfer is enabled by electron spin-orbit entanglement and electron-nuclear spin entanglement inherent within the material. Here, we demonstrate that a photon quantum state imprinted in polarization is transferred to another photon emitted from a nitrogen vacancy (NV) center. This transfer is heralded by the result of the Bell state measurement between the electron and nitrogen nuclear spins. We show that the minimum number of incident photons needed to achieve transfer is, on average, only 0.1 photons, enabling quantum teleportation over 10 km. This demonstration paves the way for a quantum repeater that is robust against phase and intensity errors, unlike the conventional photon interference scheme, thereby facilitating practical quantum networks.

Abstract Quantum state transfer is investigated beyond the nearest-neighbour coupling scheme in long spin-1/2 linear chains. Exploiting the properties of the next-nearest neighbour Hamiltonian's dispersion relation, it is shown that with minimal engineering, i.e., an on-site magnetic field on the two end sites and only a few symmetrically-modified end inter-site couplings, an average transfer fidelity above 99% can be achieved. To leading order, the required time scales linearly with the length of the chain. Such a fast, high-quality quantum state transfer is based on the ballistic propagation of the wave packet centred in the linear region of the dispersion relation by means of the on-site magnetic field. At the same time, the wave packet width, modulated by the inter-site couplings at the chain ends, whose values are found via a carefully designed genetic algorithm, is constrained mostly in the linear region of the dispersion relation. Our coupling scheme is shown to hold for arbitrary values of the next-nearest inter-site coupling and can be straightforwardly applied to longer-range coupling schemes.

Abstract A method is presented for transfer of a quantum state from one atom to another atom. In this
method, we consider the interaction of a multi-mode cavity with a multi-level quantum system and
adopt the multi-photon resonance theory for preparing an efficient quantum memory and a quantum
network. From the use of effective two- and three-level Hamiltonians, the proper values for
interaction times, coupling constants, and detunings are predicted. To examine the sensitivity of the
quantum state transfer against decoherence processes, we introduce the quantum-jump approach.
Proceeding with this approach leads to a description of the system via wavefunctions instead of density
operators and provides simple effective differential equations for obtaining analytic expressions
of the probability amplitudes.

Quantum many-body scars (QMBSs) offer a mechanism for weak ergodicity breaking, enabling nonthermal dynamics to persist in a chaotic many-body system. While most studies of QMBS focus on anomalous eigenstate properties or long-lived revivals of local observables, their potential for quantum information processing remains largely unexplored. In this work, we demonstrate that perfect quantum state transfer can be achieved in a strongly interacting, quantum chaotic spin chain by exploiting a sparse set of QMBS eigenstates embedded within an otherwise thermal spectrum. These results show that QMBSs in chaotic many-body systems may be harnessed for information transport tasks typically associated with integrable models.

ABSTRACT Scaling beyond individual quantum devices via distributed quantum computing relies critically on high‐fidelity quantum state transfers between devices, yet the quantum interconnects needed for this are currently unavailable or expected to be significantly noisy. These limitations can be bypassed by simulating ideal state transfer using quasiprobability decompositions (QPDs). Wire cutting, for instance, allows this even without quantum interconnects. Nevertheless, QPD methods face drawbacks, requiring sampling from multiple circuit variants and incurring substantial sampling overhead. While prior theoretical work showed that incorporating noisy interconnects within QPD protocols could reduce sampling overhead relative to interconnect quality, a practical implementation for realistic conditions is lacking. Addressing this gap, this work presents a generalized and practical QPD for state transfer simulation using noisy interconnects to reduce sampling overhead. The QPD incorporates a single tunable parameter for straightforward calibration to any utilized interconnect. To lower practical costs, the work also explores reducing the number of distinct circuit variants required by the QPD. Experimental validation on contemporary quantum devices confirms the proposed QPD's practical feasibility and expected sampling overhead reduction under realistic noise. Notably, the results show higher effective state transfer fidelity than direct transfer over the underlying noisy interconnect.

Coherent quantum state transfer over macroscopic distances between non-neighboring elements in quantum circuits is a crucial component to increase connectivity and simplify quantum information processing. To facilitate such transfers, an efficient and easily controllable quantum pump would be highly beneficial. In this work, we demonstrate such a quantum pump based on a one-dimensional quasicrystal Fibonacci chain (FC). In particular, we utilize the unique properties of quasicrystals to pump the edge-localized winding states between the two distant ends of the chain by only minimal manipulation of the FC at its end points. We establish the necessary conditions for successful state transfer within a fully time-dependent picture and also demonstrate robustness of the transfer protocol against disorder. We then couple external qubits to each end of the FC and establish highly adaptable functionality as a quantum bus with both on-demand switching of the qubit states and generation of maximally entangled Bell states between the qubits. Thanks to the minimal control parameters, the setup is well-suited for implementation across diverse experimental platforms, thus establishing quasicrystals as an efficient platform for versatile quantum information processing.

ABSTRACT In quantum communication, quantum state transfer from one location to another in a quantum network plays a prominent role, where the impact of noise could be crucial. The idea of state transfer can be fruitfully associated with quantum walk on graphs. We investigate the consequences of non‐Markovian quantum noises on periodicity and state transfer induced by a discrete‐time quantum walk on graphs, governed by the Grover coin operator. Different bipartite graphs, such as the path graph, cycle graph, star graph, and complete bipartite graph, present periodicity and state transfer in a discrete‐time quantum walk depending on the topology of the graph. We investigate the effect of quantum non‐Markovian dephasing noises, particularly quantum non‐Markovian Random Telegraph Noise (RTN) and modified non‐Markovian Ornstein‐Uhlenbeck Noise (OUN) on state transfer and periodicity. We demonstrate how the RTN and OUN noises allow state transfer and periodicity for a finite number of steps in a quantum walk. Our investigation brings out the feasibility of state transfer in a noisy environment.

We investigate squeezing of light through quantum-noise-limited interactions with two different material systems: an ultracold atomic spin ensemble and a micromechanical membrane. Both systems feature a light-matter quantum interface that we exploit, respectively, to generate polarization squeezing of light through Faraday interaction with the collective atomic spin precession, and ponderomotive quadrature squeezing of light through radiation pressure interaction with the membrane vibrations in an optical cavity. Both experiments are described in a common theoretical framework, highlighting the conceptual similarities between them. The observation of squeezing certifies light-matter coupling with large quantum cooperativity, a prerequisite for applications in quantum science and technology. In our experiments, we obtain a maximal cooperativity of Cqu = 10 for the spin and Cqu = 9 for the membrane. In particular, our results pave the way for hybrid quantum systems where spin and mechanical degrees of freedom are coherently coupled via light, enabling new protocols for quantum state transfer and entanglement generation over macroscopic distances.

The processes generating quantum entanglement in DNA.

This paper is a sequel to the work of Bhattacharjya et al. (2024) [2] on quantum state transfer on blow-up graphs, where instead of the adjacency matrix, we take the Laplacian matrix as the time-independent Hamiltonian associated with a blow-up graph. We characterize Laplacian strong cospectrality, periodicity, perfect state transfer (LPST) and pretty good state transfer (LPGST) on blow-up graphs. We present several constructions of blow-up graphs with LPST and produce new infinite families of regular graphs where each vertex is involved in LPST. We also determine LPST and LPGST in blow-ups of classes of trees. Finally, if n ≡ 0 (mod 4), then the blow-up of n copies of a graph has no LPST, but we show that under certain conditions, the addition of an appropriate matching to this blow-up graph results in LPST.

Perfect, pretty good and optimised quantum state transfer in transmon qubit chains

The pumped Su-Schrieffer-Heeger (SSH) model has been extensively employed for robust quantum state transfer (QST) due to its topologically protected edge channels that exhibit intrinsic resilience against local perturbations. Hybrid quantum systems have garnered significant research interest due to their unique capacity to collect distinct advantageous features that are inherently incompatible within individual physical platforms. Here, we propose a topological QST protocol for microwave (MW)-to-optical photon conversion in a synthesized SSH chain of a hybrid system. The topological structure is constructed by connecting superconducting resonators with optical cavities through interfaces of nitrogen-vacancy center ensembles. More importantly, we shorten the duration threshold of adiabatic evolution through power-law coupling engineering, and provide favorable conditions for high-efficiency MW-to-optical photon conversion, which significantly improves the scalability of the transducer with respect to both the system size and the number of converted photons. This approach paves the way for establishing high-efficiency quantum interfaces between localized MW quantum circuits and optical fiber networks, which is essential for long-distance quantum communication and distributed quantum computing.

Hadamard diagonalizable graphs are undirected graphs for which the corresponding Laplacian is diagonalizable by a Hadamard matrix. Such graphs have been studied in the context of quantum state transfer. Recently, the concept of a weak Hadamard matrix was introduced: a { − 1 , 0 , 1 } -matrix P such that P P T is tridiagonal, as well as the concept of weakly Hadamard diagonalizable graphs. We therefore naturally explore quantum state transfer in these generalized Hadamards. Given the infancy of the topic, we provide numerous properties and constructions of weak Hadamard matrices and weakly Hadamard diagonalizable graphs in order to better understand them.

We propose a scheme of an optomechanical system that optimizes entanglement in nanomechanical resonators through quantum state transfer of intracavity squeezing and squeezed reservoir field sources assisted by radiation pressure. The system is driven by red-detuned laser fields, which enable simultaneous cooling of the mechanical resonators and facilitate the quantum state transfer in a weak coupling and good cavity limit. Specifically, the mechanical entanglement is quantified using logarithmic negativity within the bipartite Gaussian states of the two mechanical modes. The results show that several key parameters, including the parametric phase and nonlinear gain of the non-degenerate optical parametric amplifier, the strength of the squeezing reservoir, optomechanical cooperativity, thermal excitation of phonons, and the temperature of mechanical baths, strongly influence the degree of mechanical entanglement. Hence, the findings indicate that careful tuning of the parameters can enable control over the enhancement of entanglement robustness, suggesting that this optomechanical scheme provides a viable pathway for applications in quantum sensing and information processing • An optomechanical scheme enhances entanglement via squeezing and red-detuned driving. • Entanglement is quantified using logarithmic negativity from the covariance matrix. • Key parameters: squeezing strength, phase, gain, cooperativity, and bath temperature. • Coupling to a two-mode squeezed vacuum boosts robustness to mechanical thermal noise. • The scheme offers a viable platform for quantum metrology and information processing.