Using quantum methods to read classical memories offers surprising advantages

Currently, the data stored in classical digital memories such as CDs, DVDs, and barcodes is read by classical light. But as a new study shows, using quantum light to read these classical memories can bring surprising advantages. Quantum light can read digital data using very few photons, an ability that could lead to faster digital readers and optical memories with larger storage capacities than before.

“This is the first demonstration showing that the use of nonclassical light is beneficial for the readout of digital memories, reminiscent of current optical storage devices,” Pirandola told

As Pirandola explains in his study, there is an important difference between classical light – the light that is used in practically all of today’s technology applications – and quantum light. In classical light, the states of the electromagnetic field can be decomposed as probabilistic sums of coherent states. In contrast, when this decomposition is not possible, the states of an electromagnetic field are considered to be nonclassical (quantum). Important examples of nonclassical states are those that are entangled, in particular those with Einstein-Podolsky-Rosen (EPR) correlations. When two modes of light are described by these kinds of entangled states, their position and momentum “quadratures” are extremely correlated with each other.

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