Distributed Quantum Information Processing: A Review of Recent Progress

TL;DR

This review surveys distributed quantum information processing as a path to scaling quantum technology by interconnecting modular nodes through quantum and classical channels. It integrates theoretical foundations (quantum channels, teleportation, and multi-copy measurement) with practical protocols (state transfer, entanglement distribution, and circuit-knitting) and maps them onto diverse platforms (neutral atoms, ions, superconductors, color centers, quantum dots, and photonics). It highlights key algorithmic advances that exploit multi-copy access, such as Bell sampling, randomized measurements, and various memory-usage schemes, while addressing verification, error mitigation, and complexity bounds under realistic communication constraints. The work emphasizes the current mid-term station of the field, the engineering bottlenecks, and the promising avenues toward fault-tolerant, distributed quantum computing with impactful implications for quantum networks, sensing, and cryptography.

Abstract

Distributed quantum information processing seeks to overcome the scalability limitations of monolithic quantum devices by interconnecting multiple quantum processing nodes via classical and quantum communication. This approach extends the capabilities of individual devices, enabling access to larger problem instances and novel algorithmic techniques. Beyond increasing qubit counts, it also enables qualitatively new capabilities, such as joint measurements on multiple copies of high-dimensional quantum states. The distinction between single-copy and multi-copy access reveals important differences in task complexity and helps identify which computational problems stand to benefit from distributed quantum resources. At the same time, it highlights trade-offs between classical and quantum communication models and the practical challenges involved in realizing them experimentally. In this review, we contextualize recent developments by surveying the theoretical foundations of distributed quantum protocols and examining the experimental platforms and algorithmic applications that realize them in practice.

Figures (10)

• Figure 1: Deterministic quantum state transfer protocols. (a) Cavity quantum electrodynamics setup with a tunable coupling $g(t)$ and cavity decay rate $\kappa$. The photon decays into the quantum link and is reabsorbed at the second node. (b) Two registers connected by a quantum spin chain that is governed by a nearest-neighbor coupling at rate $J$.
• Figure 2: Two different types of remote entanglement protocols. (Left) Detector-in-midpoint configuration where photons are sent to a beam splitter, effectively realizing a Bell-basis measurement (red region in circuit). This enables heralded entanglement generation between the systems at nodes $A$ and $B$ (indicated by gray oval shapes at the end of the circuit). (Right) Sender-receiver protocols where a conditional gate between a single photon and each of the systems at nodes $A$ and $B$ is realized. Figure adapted from Ref. beukers2024remoteentanglement.
• Figure 3: Schematic overview of distributed quantum computation with network architecture (left) and distributed quantum circuit (right). Several nodes ($N_1, \cdots,N_k$) of a quantum network are connected through quantum channels ($\mathcal{E}_{N_i,N_j}$ between nodes $N_i$ and $N_j$), i.e., communication channels which can transmit quantum information (Sec. \ref{['ssec:quantum-channels']}). The individual nodes may be realized using different physical platforms (Sec. \ref{['ssec:platforms']}) and have different connectivities (as indicated by black solid lines). The quantum channels allow the execution of nonlocal gates (orange lines both in the left and right subplots) between different nodes.
• Figure 4: Quantum teleportation protocols. (a) State teleportation of a single qubit and (b) teleportation of a controlled-NOT gate. The latter implements a CNOT operation between registers $A^\prime$ and $B^\prime$, consuming the Bell pair $\ket{\Phi_{AB}^+}$.
• Figure 5: The width and depth of a quantum circuit may be reduced using circuit-knitting techniques. In (a) gate cutting, a nonlocal circuit may be simulated by cutting it in two halves and running the resulting local circuits separately. A (b) wire cut is a technique where a qubit wire is split, and the resulting segments are simulated independently, followed by classical post-processing to recover the full circuit behavior. Circuit cutting comes at the cost of a sampling overhead.