Quantum Information Capacity and Communication Channels

The study of quantum information capacity and communication channels lies at the heart of quantum Shannon theory, which seeks to quantify the ultimate limits on information transmission when quantum effects are exploited. Unlike classical channels, quantum channels can convey not only classical bits but also qubits, entanglement and secret keys, giving rise to multiple capacity measures. Central figures include the quantum capacity (the highest rate of reliable qubit transmission), the classical capacity (the maximal rate of classical information transfer) and the private capacity (the rate of secure classical communication). These capacities are determined by entropic quantities such as coherent information and the Holevo information, and can exhibit uniquely quantum features such as superadditivity and superactivation, wherein combined channels outperform individual ones. Channel degradability and antidegradability provide criteria for single‐letter capacity formulas, while non-Gaussian noise, thermal environments and energy constraints pose significant challenges. Progress in bounding capacities for bosonic Gaussian channels, amplitude‐damping channels and thermal attenuators informs the design of quantum networks, from fibre-optic links to satellite relays, and underpins advances towards a global quantum internet.

Research from Nature Portfolio

Recent studies have focused on extending analytic capacity calculations to more complex channels. One work generalised qubit amplitude-damping channels to multi-level systems, employing degradability and data-processing inequalities to compute exact quantum and private classical capacities for finite dimensions, and further evaluated entanglement-assisted capacities across a broad class of maps. Another investigation derived tight upper bounds on the quantum capacity of thermal attenuator channels by introducing an extended degradable model and applying bottleneck inequalities to channel decompositions. These bounds significantly narrow the uncertainty on capacity for both qubit and bosonic attenuators under realistic noise and energy constraints, facilitating reliable estimates for low-noise optical and microwave links.

Quantum Information Capacity and Communication Channels publication trend

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

Technical terms

Quantum capacity: The maximum rate at which qubits can be transmitted reliably over a quantum channel.

Classical capacity: The maximum rate of classical information transfer achievable using quantum channels.

Private capacity: The rate at which classical information can be sent securely against an eavesdropper.

Degradability: A property of a channel allowing the environment’s output to be simulated from the channel output, enabling single-letter capacity formulas.

Superadditivity: A phenomenon where the combined capacity of multiple channels exceeds the sum of their individual capacities.

Zero-error capacity: The highest rate of information transmission guaranteed to be error-free under specified noise models.

References

1. Resonant Multilevel Amplitude Damping Channels. Quantum (2023).
2. Shemesh Theorem and Its Relation With the Zero-Error Quantum Information Theory. IEEE Access (2024).
3. Bounding the energy-constrained quantum and private capacities of phase-insensitive bosonic Gaussian channels. New Journal of Physics (2018).
4. Narrow bounds for the quantum capacity of thermal attenuators. Nature Communications (2018).
5. How Deep the Theory of Quantum Communications Goes: Superadditivity, Superactivation and Causal Activation. IEEE Communications Surveys & Tutorials (2022).
6. Quantum capacity analysis of multi-level amplitude damping channels. Communications Physics (2021).