Experimental Demonstration of Instrument-specific Quantum Memory Effects and Non-Markovian Process Recovery for Common-Cause Processes

Understand

The duration, strength and structure of memory effects are crucial properties of physical evolution.

• Due to the invasive nature of quantum measurement, such properties must be defined with respect to the probing instruments employed.
• Here, using a photonic platform, we experimentally demonstrate this necessity via two paradigmatic processes: future-history correlations in the first process can be erased by an intermediate quantum measurement; for the second process, a noisy classical measurement blocks the effect of history.
• We then apply memory truncation techniques to recover an efficient description that approximates expectation values for multi-time observables.