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💧 Quantum Decoherence — T1/T2 Qubit Dephasing Simulator

Watch a qubit's coherence decay live: tune T2 dephasing and T1 relaxation times and starting Bloch angle, and see the density matrix and purity Tr(ρ²) evolve in real time.

Quantum Physics2DAdvanced60 FPS

About Quantum Decoherence

Decoherence is what happens when a quantum system stops behaving quantum-mechanically because it becomes entangled with its surroundings. This simulator models a single qubit's density matrix ρ and lets you watch its off-diagonal coherence term ρ01 decay exponentially with a characteristic dephasing time T2, while its diagonal populations ρ00 and ρ11 optionally relax toward the ground state on a separate timescale T1. Both are the two standard experimental metrics engineers quote when they report how "good" a physical qubit is.

The equatorial panel shows the transverse Bloch vector shrinking as coherence is lost, the side bar tracks the vertical population balance, and the scrolling plot traces both |ρ01(t)| and the purity Tr(ρ²) over real elapsed time. Understanding and fighting decoherence — through cryogenic cooling, vacuum isolation, dynamical decoupling and quantum error correction — is the central engineering challenge standing between today's noisy qubits and a fault-tolerant quantum computer.

Frequently Asked Questions

What is quantum decoherence?

Decoherence is the loss of a quantum system's ability to show interference and superposition, caused by unavoidable interactions and entanglement with its environment. As a qubit decoheres, its off-diagonal density-matrix element ρ01 shrinks toward zero and the state starts to behave like a classical statistical mixture instead of a coherent superposition.

What do T1 and T2 mean?

T1 is the energy relaxation time — how long an excited qubit takes to decay toward its ground state. T2 is the dephasing time — how long the coherence between basis states survives. T2 is always less than or equal to twice T1, and both are standard figures of merit reported for every real quantum-computing platform.

Why does purity drop even though the populations stay fixed?

Under pure dephasing (T1 switched off) the populations ρ00 and ρ11 never change, only the coherence ρ01 decays. Purity Tr(ρ²) = ρ00² + ρ11² + 2|ρ01|² still falls because the |ρ01|² term vanishes, leaving only ρ00² + ρ11², which equals 0.5 only for an exact equal superposition (θ = 90°) and is otherwise somewhere between 0.5 and 1.

Why does this matter for quantum computers?

Every quantum algorithm relies on maintaining coherent superpositions and interference between qubits for as long as the computation takes. Decoherence is the enemy of that: it is why quantum processors are cooled in dilution refrigerators near absolute zero, isolated in vacuum and shielded from stray electromagnetic noise — all to push T1 and T2 as high as possible before the environment scrambles the state.

⚙ Under the hood

Watch a qubit's coherence decay live: tune T2 dephasing and T1 relaxation times and starting Bloch angle, and see the density matrix and purity Tr(ρ²) evolve in real time.

Canvas 2DQubitBloch SphereDecoherenceDensity Matrix

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install