Kavli Affiliate: Simon Groblacher
| First 5 Authors: Soroush Khademi, Soroush Khademi, , ,
| Summary:
Weak quantum measurements enable real-time tracking and control of dynamical
quantum systems, producing quantum trajectories — evolutions of the quantum
state of the system conditioned on measurement outcomes. For classical systems,
the accuracy of trajectories can be improved by incorporating future
information, a procedure known as smoothing. Here we apply this concept to
quantum systems, generalising a formalism of quantum state smoothing for an
observer monitoring a quantum system exposed to environmental decoherence, a
scenario important for many quantum information protocols. This allows future
data to be incorporated when reconstructing the trajectories of quantum states.
We experimentally demonstrate that smoothing improves accuracy using a
continuously measured nanomechanical resonator, showing that the method
compensates for both gaps in the measurement record and inaccessible
environments. We further observe a key predicted departure from classical
smoothing: quantum noise renders the trajectories nondifferentiable. These
results establish that future information can enhance quantum trajectory
reconstruction, with potential applications across quantum sensing, control,
and error correction.
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