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.
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.
The transport of states is a fundamental task in quantum information processing systems, enabling operations such as quantum key distribution and inter-component communication within quantum computers. A straightforward approach to the design of state transfer networks are spatial symmetries such as permutation or reflection symmetry. Instead of strictly confining the design space in this fashion, our work takes a novel path by harnessing photonic networks that lack any conventional spatial symmetries, while nevertheless supporting an efficient transfer of quantum states [1], [2]. Key to this approach are so-called latent symmetries [3], which are embodied exclusively in the spectral properties of the network, thereby remaining hidden in the spatial domain. Two network sitesuandvare considered latent-symmetric if there is no permutation symmetry between them, but the two sites are cospectral, i.e. the sets of eigenvalues of the networks obtained upon removal of either site are identical (fig. 1a). One of the hallmark features of latent symmetry is the existence of so-called singlet sites [4] at which these networks can be arbitrarily extended without breaking the latent symmetry (e.g. for sitesa,b,cin fig. 1a). Anti-symmetric excitations at the two latent-symmetric sites will always interfere destructively at those singlet sites and hence will never leave the initial network. Latent symmetries significantly improve the flexibility in designing quantum networks and hold great potential for applications in quantum cryptography and secure state transfer.
Quantum networks intersect a paradigmatic shift in communication technologies, offering unprecedented capabilities for secure communication and distributed computation through the exploitation of quantum mechanical phenomena.These networks facilitate revolutionary and unlimited of possibility applications such as quantum key distribution (QKD), distributed quantum computing (DQC), quantum teleportation (QT), quantum clock synchronization (QCS), etc. -all fundamentally predicated on quantum entanglement as their operational cornerstone.Moreover, on the contrary with classical computer communication protocol, quantum networks have the fundamental no-cloning theorem in the quantum mechanic prohibits conventional signal amplification techniques, necessitating the development of quantum-native routing strategies that operate within these unique constraints.However, the practical realization of quantum networks until now still faces a crucial challenge: The reliability and efficient distribution of highfidelity entangled quantum states across long distances.Due to this distribution, the process faces intrinsic limitations arising from quantum decoherence, photonic loss in transmission channels, and the inherently probabilistic nature of entanglement generation protocols.In quantum communication, fidelity serves as a fundamental metric, representing the degree of similarity or correlation between the actual distributed entangled state and an ideal maximally entangled Bell pair.Fidelity is a crucial measure of the quality of quantum states in a network since it directly affects the reliability and effectiveness of quantum communication protocols.High fidelity ensures that the transmitted entangled states maintain their quantum properties, closely resembling the ideal Bell pair, and are thus suitable for performing secure and efficient quantum operations.Latency, on the other hand, refers to the total time delay involved in the entire process of entanglement establishment, from the initial creation of the entangled pairs to the final verification and confirmation of the entanglement quality.This includes several distinct components: the physical propagation delay, which accounts for the time it takes for quantum information to travel through the communication channel (such as optical fibers); the entanglement generation time, which involves the probabilistic creation of entangled states between quantum nodes; and the quantum memory storage time, which reflects the duration for which quantum states I
Integrated quantum photonics hold the promise to scale up the system size and form an on-chip quantum network with distributed information processing and simulation units. An outstanding need of such quantum network is to have high fidelity and efficiency on-chip state transfer between distant nodes. Although the nodes are naturally connected via waveguides, it is challenging to fulfill this need because stringent conditions such as spatial mode-matching configuration and time-reversal symmetry have to be satisfied. Here we report a type of quantum photonic nodes consisting of single quantum emitters and cascaded microring resonators for on-chip state transfer. By interfacing the node with a waveguide, we show that all the emission from the node can be funneled into the waveguide and its temporal profile can be synthesized to be time-reversal symmetric. We demonstrate theoretically on-chip quantum state transfer between two distant nodes with near-unity overall success rate can be achieved without any dynamic control. Moreover, we discuss the experimental implementation of our scheme with CMOS compatible integrated photonic platforms and solid-state quantum optics techniques.
Hybrid integrated quantum photonic circuits have the potential to scale up the number of quantum nodes and to build a network with distributed quantum-information-processing units at affordable resources. A central need of such systems is to have near-unity success-rate state transfer between the quantum nodes. This turns out to be a grand challenge since stringent conditions of spatial mode matching and time-reversal symmetry between the sending and receiving nodes have to be simultaneously satisfied. Here we devise a type of hybrid quantum node consisting of a single solid-state quantum system and a coupled-cavity structure toward achieving perfect state transfer between two distant nodes connected via waveguides. The hybrid node possesses flexibility in tailoring the temporal profile of the emitted single-photon wave packet without any dynamic modulation. In particular, we show it could emit time-reversal symmetric single-photon wave packets and fully couple the emission to the waveguide, fulfilling the conditions for perfect quantum state transfer. We develop a complete theoretical framework and provide a clear physical picture of the protocol for transferring a superposition state. We show ideally the simple node structures with one, two, and three chain-coupled microring resonators could lead to total success rates of 90.5%, 97.5%, and 99.3%, respectively. We then further discuss the influence of imperfections and experimental realizations of our scheme with integrated quantum photonics.
We propose modulation protocols designed to generate, store, and transfer compact localized states in a quantum network. Induced by parameter tuning or local reflection symmetries, such states vanish outside selected domains of the complete system and are therefore ideal for information storage. Their creation and transfer is here achieved either via amplitude phase flips or via optimal temporal control of intersite couplings. We apply the concept to a decorated, locally symmetric Lieb lattice where one sublattice is dimerized, and also demonstrate it for more complex setups. The approach allows for a flexible storage and transfer of states along independent paths in lattices supporting flat energetic bands. We further demonstrate a method to equip any network featuring static perfect state transfer of single-site excitations with compact localized states, thus increasing the storage ability of these networks. We show that these compact localized states can likewise be perfectly transferred through the corresponding network by suitable, time-dependent modifications. The generic network and protocols proposed can be utilized in various physical setups such as atomic or molecular spin lattices, photonic waveguide arrays, and acoustic setups.
Quantum entanglement is crucial for quantum information processing, prominently used in quantum communication, computation, and metrology. Recent studies have shifted toward high-dimensional entangled states, offering greater information capacity and enabling more complex applications. Here, we experimentally prepared a three-photon asymmetric maximally entangled state, comprising two two-dimensional photons and one four-dimensional photon. Using this state, we conducted a proof-of-principle experiment, successfully transferring a four-dimensional quantum state from two photons to another photon with fidelities ranging from 0.78 to 0.86. These results exceed theoretical limits, demonstrating genuine four-dimensional quantum state transfer. The asymmetric entangled state demonstrated here holds promise for future quantum networks as a quantum interface facilitating information transfer across quantum systems with different dimensions.