Quantum Information, Computation and Communication

Quantum information science studies how information can be represented, manipulated and transmitted using quantum systems. At its core is the qubit: a two-level system that, unlike a classical bit, can exist in superposition and become entangled with others. Quantum gates—unitary operations on qubits—implement algorithms that in some cases outperform the best known classical protocols. Quantum communication harnesses entanglement and the no-cloning theorem to realise unconditionally secure key exchange, superdense coding of classical bits into qubits, and teleportation of quantum states. In computation, amplitude amplification and phase-estimation subroutines underpin algorithms for search, simulation and factoring, promising exponential or quadratic speed-ups. Practical progress relies on high-fidelity gate operations, robust error-correction schemes and precise state and process tomography to benchmark and verify devices. Recent advances in scalable hardware—ranging from superconducting circuits to photonic platforms—have ushered in the NISQ era, where tens to hundreds of qubits perform tasks beyond classical reach. Looking forward, the convergence of quantum information with advances in networking and error control paves the way for fault-tolerant quantum computers and distributed quantum protocols that may transform computing, cryptography and sensing.

Research from Nature Portfolio

Innovations in quantum process tomography have dramatically extended the reach of device characterization. A hybrid approach combining tensor-network ansätze with unsupervised machine-learning has been used to reconstruct the full process matrices of up to ten-qubit random circuits with fidelities exceeding 99 %, using orders of magnitude fewer measurement settings than traditional methods. Another breakthrough addressed the challenge of multi-hypothesis channel discrimination by showing that entangled photons, together with generalised nulling receivers, can outperform all classical strategies when identifying the position of a target channel among many background channels. This entanglement-enhanced receiver not only extends quantum hypothesis testing beyond binary decisions but also promises applications in optical data-readout and spectroscopic multiplexing. Foundational work on quantum key repeaters has further established fundamental limits on the rates at which secure key material can be distilled from noisy entangled states, revealing trade-offs that guide the design of long-range quantum networks.

Research from all publishers

A novel “Fourier quantum process tomography” scheme has been proposed to simplify characterization of unknown optical transformations. By measuring probability distributions in two conjugate bases and applying phase-retrieval algorithms, this method reconstructs process matrices with near-minimal measurement sets and reports average fidelities above 90 %—all with significant computational savings over maximum-likelihood estimation. In parallel, a data-driven approach to quantum process tomography has leveraged Kraus-operator representations and gradient-descent optimization on Stiefel manifolds to learn low-rank descriptions of multi-qubit channels. This method matches or exceeds the performance of both compressed-sensing and projected least-squares techniques, reconstructing processes with just a few random measurements while scaling efficiently to five-qubit systems. Together, these techniques promise practical diagnostics for intermediate-scale quantum devices.

Quantum Information, Computation and Communication publication trend

The graph below shows the total number of articles in quantum information, computation and communication across all publications each year (not limited to Nature Index journals).

Technical terms

Qubit: The fundamental unit of quantum information, able to occupy superpositions of logical states |0⟩ and |1⟩.

Quantum gate: A reversible unitary operation on one or more qubits, generalising classical logic gates to the quantum domain.

Entanglement: A nonclassical correlation between quantum systems in which the joint state cannot be factored into independent parts.

Quantum channel: A completely positive, trace-preserving map describing noise and loss in the transmission or processing of quantum states.

Tomography: A procedure for reconstructing an unknown quantum state or process by measuring a series of observables.

Fidelity: A measure of the overlap between two quantum states or processes, indicating how closely an implementation matches the ideal.

References

1. Quantum process tomography with unsupervised learning and tensor networks. Nature Communications (2023).
2. Fourier Quantum Process Tomography. npj Quantum Information (2024).
3. Gradient-Descent Quantum Process Tomography by Learning Kraus Operators. Physical Review Letters (2023).
4. Entanglement-enhanced testing of multiple quantum hypotheses. Communications Physics (2020).
5. Limitations on quantum key repeaters. Nature Communications (2015).