Algorithms
Classical Shadow
An efficient technique for extracting useful classical information from a quantum state using relatively few measurements.
Definition
Classical shadows are a measurement technique that allows researchers to estimate many different properties of a quantum state using a relatively small number of randomized measurements, rather than needing a separate, large set of measurements for each property of interest.
Technical Definition
Introduced by Huang, Kueng, and Preskill in 2020, the technique constructs an efficiently storable classical approximation ('shadow') of a quantum state from randomized measurement data, from which many different observable properties can later be estimated without needing to re-run the quantum experiment.
Visual Explanation: An Analogy
Think of classical shadows like taking a few cleverly chosen photographs of a complex 3D object from different random angles, then being able to estimate many different facts about the object's shape later, without needing to physically examine it again from every possible angle.
Real-World Use Cases
- Used to reduce the number of measurements needed when characterizing or verifying quantum states and processes
- An active area of research for making near-term quantum experiments more measurement-efficient