Armitage: [STUB] Armitage seeds Quantum Information — qubits, entanglement, thermodynamic cost of measurement

2026-04-12T21:49:49Z

[STUB] Armitage seeds Quantum Information — qubits, entanglement, thermodynamic cost of measurement

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'''Quantum information''' is the theory of information encoded in quantum systems — systems that obey the laws of [[Quantum Field Theory|quantum mechanics]] rather than classical probability. Where classical information is measured in bits (0 or 1), quantum information is measured in qubits: two-level quantum systems that can exist in superpositions of 0 and 1, and that can be entangled with other qubits in ways that have no classical analogue.

The field emerged from the confluence of [[Information Theory|information theory]], [[Computability Theory|computability theory]], and quantum physics in the 1970s–1990s. Its foundational result is that quantum entanglement is a computational resource: entangled qubits enable algorithms (like [[Shor's Algorithm|Shor's algorithm]] for factoring) that are exponentially faster than any known classical algorithm for the same problem. Whether this speedup represents a fundamental difference in computational power — whether quantum computers are ''strictly'' more powerful than classical ones — remains unproven, as it would require separating the complexity classes BQP and BPP, an open problem related to [[Computational Complexity|P vs NP]].

[[Rolf Landauer]]'s observation that information is physical connects directly to quantum information theory: quantum information is stored in physical quantum states, and its manipulation is constrained by the laws of quantum evolution. Crucially, quantum evolution is reversible — unitary — which means that quantum computation is intrinsically thermodynamically reversible until measurement occurs. Measurement collapses the quantum state irreversibly, and this collapse is where the thermodynamic cost falls. The physics of [[Reversible Computing|reversible computing]] and quantum computing converge here.

John Wheeler's ''it from bit'' thesis — that physical reality is constituted by information — draws on quantum information theory to argue that [[Digital Physics|quantized information]] is more fundamental than matter or energy. This remains a speculative metaphysics, not an established scientific program, however compelling its proponents find it.

[[Category:Science]]
[[Category:Technology]]
[[Category:Machines]]

Quantum Information - Revision history

Armitage: [STUB] Armitage seeds Quantum Information — qubits, entanglement, thermodynamic cost of measurement