The Quantum Applications Landscape: 5 Groups, and Where Does QKD Fit?
Say “quantum technology” and most people picture a quantum computer. In reality it is an ecosystem of several distinct application groups, each with its own problems, software, and hardware. I put together the five groups below while preparing my seminar on “Quantum Internet in the Sky”.
| Application Group | Representative Software | Representative Hardware |
|---|---|---|
| Quantum Security | QKD (BB84), liboqs, CRYSTALS-Kyber/Dilithium | QRNG chips, single-photon detectors, QKD devices |
| Quantum Communication | NetQASM, QuNetSim, entanglement distribution protocols | Quantum memory nodes, entangled photon sources, QKD satellites (Micius) |
| Quantum-Inspired | D-Wave Leap, TensorFlow Quantum, simulated annealing/branching solvers | Fujitsu Digital Annealer, Toshiba SBM |
| QC & Simulation | Qiskit, PennyLane, Q#, QuTiP | Superconducting qubits (IBM/Google), trapped ions (IonQ) |
| Quantum Sensing | Sensor fusion algorithms, VLBI signal processing | Optical lattice clocks, NV-center magnetometers, atom interferometers |
Quantum Security uses quantum principles to protect information: generating truly random numbers with a QRNG, distributing keys with unconditional security through QKD, or running post-quantum cryptography such as CRYSTALS-Kyber on ordinary classical hardware, now a NIST standard as of 2024. Quantum Communication takes a different angle, using quantum principles to transmit quantum information itself, qubits and entangled states, between nodes. This is the foundation for a future Quantum Internet, one built not just to share keys but to support distributed quantum computation.
The remaining two groups on the computing side are a different animal entirely. Quantum-Inspired algorithms borrow ideas from quantum mechanics, annealing and simulated branching among them, but run on specialized classical hardware, with no real qubits involved, and they are still effective at combinatorial optimization. QC & Simulation is where actual quantum computers live, built on superconducting qubits or trapped ions, alongside the SDKs used to program and simulate quantum algorithms on them. Quantum Sensing, meanwhile, exploits the extreme sensitivity of quantum states for precise measurement of magnetic fields, time, or distance, with applications spanning astronomical VLBI to navigation where GPS is unavailable.
So where does QKD actually belong
Here is the interesting part: QKD does not fit neatly into a single group. In terms of purpose, it is a security problem, generating and sharing a key that stays secure. In terms of mechanism, though, it is a communication problem, since it requires faithfully transmitting and measuring qubit states across distance, exactly the infrastructure a Quantum Internet needs regardless of what it is ultimately used for.
This is exactly why my own research, modeling satellite FSO channels for QKD, is both a key-security problem and a building block for satellite quantum communication infrastructure more broadly. Two groups that look separate on paper turn out to share the same physical layer underneath.