Spectroscopy techniques exploiting quantum effects to study atomic and material properties.Quantum spectroscopy refers to techniques that exploit quantum mechanical properties of light or matter—such as entanglement, squeezing, or discrete energy levels—to probe the structure and dynamics of atoms, molecules, and materials with sensitivities or resolutions beyond classical limits. It encompasses methods like entangled-photon spectroscopy, where correlated photon pairs reveal information about a sample that would be obscured by classical noise, and quantum-enhanced Raman or absorption spectroscopy, which use non-classical light to beat the shot-noise limit.
In classical spectroscopy, light interacts with a sample, and the transmitted or scattered light reveals absorption or emission features. Quantum spectroscopy often uses non-classical light states: for example, entangled photon pairs can be used in 'induced coherence' setups where one photon probes the sample and the other carries the information, suppressing background noise. Alternatively, squeezed light reduces intensity fluctuations below the quantum limit, improving signal-to-noise in absorption measurements. The technique relies on precise control of quantum states and detection, often involving single-photon detectors and coincidence counting.
Quantum spectroscopy is being developed for ultra-sensitive trace-gas detection, biological imaging with low light levels to avoid photodamage, and characterizing quantum materials and devices.
| dN/dE | variable | Differential number of particles per energy interval — particle spectrum joule per joule |
| E | variable | Particle energy — energy joule |
| alpha | variable | Spectral index of the power law |
| E_cut | variable | Cutoff energy — energy joule |
| P | variable | Power — power watt |
| N | variable | Number of atoms — particle number |
| X_n | variable | random variable indexed by n — random variable |
| d_s | variable | spectral dimension — spectral dimension |
| Var | operator | statistical variance of a random variable — variance |
| ~ | operator | asymptotically proportional to (up to a constant factor) — asymptotic equivalence |
| f | operator | some function of the spectral dimension — function |
| n_s | variable | Scalar spectral index — scalar spectral index |
| \epsilon | variable | First slow-roll parameter — slow roll parameter |
| \eta | variable | Second slow-roll parameter — slow roll parameter second |
| r | variable | Tensor-to-scalar ratio — tensor to scalar ratio |
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