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Guang-Can Guo co-supervised and helped design a photon-based dephasing simulator, using controlled initial polarization–frequency correlations to investigate open quantum system dynamics.^[ref]

A physicist working on quantum information. Affiliation recorded at publication in 2018: University of Science and Technology of China, CAS Key Laboratory of Quantum Information.^[ref]

An open quantum system interacts with degrees of freedom treated as an environment. If system and environment jointly have density matrix ${\rho }_{SE}$, the system state is the partial trace ${\rho }_S={\mathrm{Tr}}_E{\rho }_{SE}$. Even unitary joint evolution can change the system's purity because correlations with the environment are discarded.

For example, an interaction mapping $|0⟩|e⟩$ to $|0⟩|e_0⟩$ and $|1⟩|e⟩$ to $|1⟩|e_1⟩$ multiplies the system coherence by $⟨e_1|e_0⟩$. Distinguishable environment states suppress that coherence. A time-local memoryless master equation is an additional approximation, not part of the definition of an open system.

Quantum dynamics describes the time evolution of a quantum state and its observable predictions. For an isolated system with Hamiltonian operator $H$, the Schrödinger equation is $i\hslash {\partial }_t|\psi ⟩=H|\psi ⟩$. Equivalently, a density matrix satisfies $i\hslash \dot{\rho }=[H,\rho ]$.

For time-independent $H$, the evolution operator is $U(t)=e^{-iHt/\hslash }$. An energy eigenstate changes only by a global phase, whereas a superposition develops relative phases and can display oscillating observables. Interaction with an unobserved environment generally requires open quantum system dynamics rather than a unitary evolution for the subsystem alone.

Sabrina Maniscalco co-supervised the theoretical analysis of an optical dephasing simulator, connecting controlled polarization–frequency preparation with the dynamics of an open quantum system.^[ref]

A physicist working on quantum information. Affiliation recorded at publication in 2018: University of Turku, Turku Centre for Quantum Physics; Aalto University, Department of Applied Physics.^[ref]