Glossary

The terms below are organized by working definition, common boundary cases, and the main places where they are used. Each entry keeps only the distinctions needed for quick reference; the full physical picture, formulas, scales, and references are in the corresponding chapters.

Data, Statistics, and Inference

Term	Usage in this book	Main locations
Event table	A photon-by-photon record containing at least time and detection channel, and often frequency, polarization, position, quality flag, and weight. It is not the same object as a binned light curve.	Chapters Mathematical and Physical Foundations, Detectors, clocks, and event tables, and Data analysis for event tables.
Light curve	A projection of the event table onto the time axis, usually discarding channel, polarization, and inter-event information.	Chapters Why quantum astronomy is needed and Data analysis for event tables.
Exposure function	A function describing how effective observing time, area, efficiency, and selection vary with time or channel.	Chapters Data analysis for event tables and Observing design, error budgets, and feasibility calculations.
Live time	Effective integration time after removing dead time, bad weather, saturation, and quality cuts.	Chapters Detectors, clocks, and event tables and Observing design, error budgets, and feasibility calculations.
Poisson process	A counting model in which events arrive independently once the instantaneous rate is specified; non-stationary sources require a time-dependent rate.	Chapters Mathematical and Physical Foundations, Data analysis for event tables, and Common pitfalls.
Cox process	A Poisson process whose rate is itself stochastic; it can produce super-Poisson counts without invoking new physics.	Chapter Common pitfalls.
Likelihood	The probability density or probability mass for the observed data at fixed model parameters. It should not be confused with the posterior.	Chapters Data analysis for event tables and Observing design, error budgets, and feasibility calculations.
Posterior	The parameter distribution obtained by combining likelihood and prior. Reports of posteriors should state both the prior and the data vector.	Chapters Data analysis for event tables and Teaching experiments and computational experiments.
Fisher information	A measure of the local sensitivity of the likelihood to a parameter; it is not an automatic substitute for a systematic-error model.	Chapters Mathematical and Physical Foundations, Data analysis for event tables, and Quantum estimation, the Rayleigh limit, and sub-resolution information.
Covariance matrix	A matrix describing correlations among data points or parameter errors. Multi-baseline $	V
Fano factor	The ratio of count variance to count mean, useful for diagnosing slow source variability, dead time, and afterpulsing.	Chapter Common pitfalls, Eq. (359).
Trial factor	The global-significance correction caused by multiple testing. Time bins, frequency channels, baselines, and target counts can all contribute.	Chapter Common pitfalls.
Null test	A check designed to remove the astrophysical signal while retaining instrumental or background structure, such as a time-shift, off-source, off-band, or crossed-polarization test.	Chapters Data analysis for event tables, Teaching experiments and computational experiments, and Common pitfalls.

Quantum Optics and Coherence Functions

Term	Usage in this book	Main locations
Mode	A distinguishable degree of freedom of the optical field, such as a spatial, temporal, frequency, or polarization mode. Mode number controls how strongly bunching contrast is diluted.	Chapters Foundations of quantum optics and Photon statistics and coherence functions.
Occupation number	Mean photon number in a single mode; it is often large in radio astronomy and very small for one optical astronomical mode.	Chapters Foundations of quantum optics and The quantum language of astrophysical radiation mechanisms.
Coherent state	An ideal optical state with Poisson photon-number distribution and \(g^{(2)}(0)=1\). Astrophysical laser or maser candidates are not automatically stable coherent states.	Chapters Foundations of quantum optics and Common pitfalls.
Thermal state	A chaotic optical field with bunching in a single mode; multimode averaging and finite response lower the observed contrast.	Chapters Foundations of quantum optics and Photon statistics and coherence functions.
Squeezed state	A field state in which one quadrature has noise below the vacuum level and the conjugate quadrature has increased noise; related language also appears in cosmological perturbations.	Chapters Foundations of quantum optics and Quantum questions in cosmology.
Density matrix	The state object for pure or mixed states; especially natural when astronomical light is a mixture of many unresolved components.	Chapters Foundations of quantum optics and Quantum network telescopes.
Decoherence	Loss of usable phase relations through environment, averaging, or unobserved degrees of freedom; it should not be reduced to “not quantum.”	Chapters Foundations of quantum optics and Quantum questions in cosmology.
First-order coherence function	The field-amplitude correlation; amplitude interferometry and complex visibility depend on it.	Chapters Photon statistics and coherence functions and Spatial coherence and intensity interferometry.
Second-order coherence function	The intensity or detection-event correlation; the central observable for HBT and photon statistics.	Chapters Photon statistics and coherence functions and Data analysis for event tables.
Bunching	A positive second-order correlation excess near zero delay, characteristic of thermal or chaotic light.	Chapters Mathematical and Physical Foundations and Photon statistics and coherence functions.
Antibunching	A nonclassical photon-statistics signature with \(g^{(2)}(0)<1\); very difficult to preserve in astronomical environments.	Chapters Photon statistics and coherence functions and Common pitfalls.
Coherence time	The temporal width over which first-order coherence is appreciable, usually set by spectral bandwidth.	Chapters Mathematical and Physical Foundations and Photon statistics and coherence functions.
Siegert relation	The relation, valid for thermal light or Gaussian fields, connecting second-order correlation to the squared modulus of first-order coherence.	Chapters Mathematical and Physical Foundations, Photon statistics and coherence functions, and Spatial coherence and intensity interferometry.
Glauber correlation	A quantum-optical correlation function defined with detection operators; it underlies the \(g^{(n)}\) notation.	Chapters Foundations of quantum optics and Photon statistics and coherence functions.

Interferometry, Imaging, and Mode Measurements

Term	Usage in this book	Main locations
Complex visibility	The normalized Fourier component of the sky brightness distribution; both amplitude and phase are first-order coherence information.	Chapters Mathematical and Physical Foundations and Spatial coherence and intensity interferometry.
Baseline	The vector separation between two telescopes; the visibility depends on the sky-projected component \(B_\perp\).	Chapter Spatial coherence and intensity interferometry.
\(u,v\) coverage	Sampling of the spatial-frequency plane; it controls imaging fidelity and model degeneracy.	Chapters Spatial coherence and intensity interferometry and Observing design, error budgets, and feasibility calculations.
VCZ theorem	The theorem connecting the sky brightness of an incoherent far-field source to first-order spatial coherence.	Chapter Spatial coherence and intensity interferometry and Appendix Reading Routes and Validity Boundaries for Core Relations.
Uniform disk	The simplest model for a stellar angular diameter; real stars often require limb darkening or departures from spherical symmetry.	Chapters Mathematical and Physical Foundations, Spatial coherence and intensity interferometry, and Stars as quantum light sources.
Limb darkening	The decrease of stellar-disk brightness toward the limb, which changes the visibility curve and the interpretation of angular diameter.	Chapter Stars as quantum light sources.
Intensity interferometry	Measurement of $	V
Zero-baseline contrast	The correlation-peak amplitude before spatial resolution suppresses it, often used to calibrate instrumental dilution.	Chapters Spatial coherence and intensity interferometry and Observing design, error budgets, and feasibility calculations.
Phase loss	The loss of direct complex phase information when only $	V
Phase retrieval	The algorithmic problem of recovering phase from intensity or $	V
SPADE	Spatial-mode demultiplexing: a measurement idea that projects a focal-plane field onto spatial modes to estimate sub-Rayleigh separations.	Chapters Quantum estimation, the Rayleigh limit, and sub-resolution information and Teaching experiments and computational experiments.
Rayleigh curse	The drop in Fisher information for estimating the small separation of two sources with direct imaging; it is not a limit on all measurements.	Chapters Quantum estimation, the Rayleigh limit, and sub-resolution information and Common pitfalls.
Quantum Fisher information	The upper bound on parameter information over an allowed measurement set; it is reachable only when the model and measurement assumptions are satisfied.	Chapter Quantum estimation, the Rayleigh limit, and sub-resolution information.

Instruments, Detectors, and Calibration

Term	Usage in this book	Main locations
SPAD	Single-photon avalanche diode, useful for time-tagged photon counting; dead time and afterpulsing must be modeled.	Chapter Detectors, clocks, and event tables.
PMT	Photomultiplier tube, often used for fast photon counting and Cherenkov instruments; gain, pulse shape, and background require calibration.	Chapters Detectors, clocks, and event tables and Observing design, error budgets, and feasibility calculations.
TDC	Time-to-digital converter, which turns detector pulses into digital time tags.	Chapters Detectors, clocks, and event tables and Teaching experiments and computational experiments.
Jitter	Timing scatter introduced by the detection and timing chain, broadening correlation peaks and diluting contrast.	Chapter Detectors, clocks, and event tables.
Dead time	The interval after one event during which a detector or electronic chain cannot record a new event.	Chapters Detectors, clocks, and event tables and Common pitfalls.
Afterpulsing	Delayed spurious events caused by trap release inside a detector, producing positive short-delay correlations.	Chapters Detectors, clocks, and event tables and Common pitfalls.
Dark counts	Detection events in the absence of astrophysical photons; temperature and bias voltage can change them.	Chapter Detectors, clocks, and event tables.
Electronic crosstalk	Contamination of one channel by the electronic pulse of another, potentially mimicking a zero-delay correlation.	Chapters Detectors, clocks, and event tables and Common pitfalls.
White Rabbit	A network-synchronization technology capable of sub-ns timing; adequacy depends on correlation-peak width and the baseline model.	Chapter Detectors, clocks, and event tables.
Spectral channel	A frequency or wavelength label in the event table; narrower channels increase coherence time but reduce per-channel photon number.	Chapters Detectors, clocks, and event tables and From white paper to research plan.
Polarization channel	A polarization label in the event table, used to separate source physics, scattering, Faraday effects, and instrumental polarization.	Chapters Detectors, clocks, and event tables and Dark matter, axions, and polarization quantum channels.
Calibrator star	A reference star used to determine zero-baseline contrast, system response, or angular-diameter scale.	Chapters Observing design, error budgets, and feasibility calculations and From white paper to research plan.
Systematic floor	A lower error bound that no longer improves as \(T^{-1/2}\) when integration time is increased.	Chapters Observing design, error budgets, and feasibility calculations and Common pitfalls.

Astrophysical Sources and Radiation Mechanisms

Term	Usage in this book	Main locations
Brightness temperature	Radiation intensity expressed as an equivalent blackbody temperature; very high brightness temperature often points to coherent emission or an extremely small angular scale.	Chapter The quantum language of astrophysical radiation mechanisms.
Thermal radiation	Radiation controlled by temperature and optical depth; optical stellar light is approximately thermal but not a perfect blackbody.	Chapters The quantum language of astrophysical radiation mechanisms and Stars as quantum light sources.
Synchrotron radiation	Radiation from relativistic electrons in magnetic fields, usually polarized and nonthermal.	Chapters The quantum language of astrophysical radiation mechanisms and Black holes, accretion disks, and photon rings.
Inverse Compton scattering	The process by which energetic electrons boost low-energy photons to higher energies.	Chapter The quantum language of astrophysical radiation mechanisms.
Maser	Microwave or radio stimulated-emission source, often controlled in astrophysical environments by velocity coherence and pump fluctuations.	Chapters The quantum language of astrophysical radiation mechanisms and Common pitfalls.
Natural laser	A possible optical or near-infrared stimulated-emission candidate in an astrophysical environment; not the same as a stable laboratory laser cavity.	Chapters First-generation quantum-astronomy science cases and Common pitfalls.
Broad-line region	The gas region producing broad emission lines in an AGN, constrained jointly by time delay, spectra, and angular scale.	Chapter Black holes, accretion disks, and photon rings.
Photon ring	Fine structure near a black hole produced by paths associated with photon orbits in strong gravity.	Chapter Black holes, accretion disks, and photon rings.
Type Ia supernova	A thermonuclear supernova used as a distance indicator; the intensity-interferometry scheme focuses on the photospheric angular radius.	Chapters Explosions, transients, and multi-messenger quantum astronomy and Teaching experiments and computational experiments.
Kilonova	An r-process transient following a binary-neutron-star merger; multi-messenger delay and diffusion time are key quantities.	Chapter Explosions, transients, and multi-messenger quantum astronomy.
GRB afterglow	Multiwavelength emission produced as a gamma-ray-burst jet interacts with its environment.	Chapter Explosions, transients, and multi-messenger quantum astronomy.
TDE	A tidal-disruption event, in which a star is torn apart by a black hole; it can constrain black-hole mass and the reprocessing photosphere.	Chapter Explosions, transients, and multi-messenger quantum astronomy.

Propagation, Cosmology, and New Physics

Term	Usage in this book	Main locations
DM	Dispersion measure, the frequency-dependent delay caused by electron column density.	Chapter Propagation effects: plasma, dust, and gravitational lensing.
RM	Rotation measure, the Faraday polarization rotation produced by magnetized plasma.	Chapters Propagation effects: plasma, dust, and gravitational lensing and Dark matter, axions, and polarization quantum channels.
Scattering broadening	Multipath propagation that broadens a pulse or correlation peak and can hide intrinsic time structure.	Chapter Propagation effects: plasma, dust, and gravitational lensing.
Extinction	Flux reduction by dust absorption and scattering; it affects photon rate and color.	Chapter Propagation effects: plasma, dust, and gravitational lensing.
Lens equation	The relation among source position, image position, and deflection angle.	Chapter Propagation effects: plasma, dust, and gravitational lensing.
Time-delay distance	The distance combination entering time-delay cosmology with strong lenses.	Chapter Propagation effects: plasma, dust, and gravitational lensing.
Wave-optics lensing	Lensing in the regime where wavelength, lens mass, and path difference make interference non-negligible.	Chapters Propagation effects: plasma, dust, and gravitational lensing and Dark matter, axions, and polarization quantum channels.
Axion birefringence	A candidate effect in which a light field coupling changes polarization angle with time or direction.	Chapters Dark matter, axions, and polarization quantum channels and Quantum questions in cosmology.
CMB B modes	The curl-like component of CMB polarization, produced by gravitational waves, lensing, or systematics.	Chapter Quantum questions in cosmology.
Cosmic variance	The large-scale statistical uncertainty caused by observing only one universe.	Chapter Quantum questions in cosmology.
Standard siren	A source whose gravitational-wave signal gives distance directly, then combines with redshift or an electromagnetic counterpart for cosmology.	Chapter Explosions, transients, and multi-messenger quantum astronomy.

Quantum Networks and Program Management

Term	Usage in this book	Main locations
Quantum-network telescope	A future architecture in which entanglement, quantum memories, frequency conversion, or local mode measurements assist long-baseline interferometry.	Chapters Quantum network telescopes and From white paper to research plan.
Entanglement distribution rate	The usable number of entangled resources supplied by a network per second; link loss suppresses it rapidly.	Chapter Quantum network telescopes.
Quantum memory	A device that stores quantum states or entanglement resources; storage time must cover baseline light-travel time and processing delay.	Chapter Quantum network telescopes.
Bell fidelity	The fidelity between the actual entangled state and an ideal Bell state, used as a measure of network-resource quality.	Chapter Quantum network telescopes.
Frequency conversion	Conversion of astronomical light or laboratory quantum resources into bands that can be transmitted, stored, or detected.	Chapter Quantum network telescopes.
Readiness	A quantitative judgment of whether the observable, instrument metric, calibration, code, and data products are mature enough for execution.	Chapter From white paper to research plan.
Milestone	A project step with an observable, target precision, deadline, null test, and data deliverable.	Chapter From white paper to research plan.
Data product	A reusable deliverable such as an event table, correlation histogram, $	V
Risk register	A project table listing technical risks, science risks, probabilities, impacts, and mitigation plans.	Chapter From white paper to research plan.
Failure criterion	A pre-defined condition for stopping or downgrading a project, such as a target being too faint, a systematic floor being too high, or a trigger arriving too late.	Chapters Observing design, error budgets, and feasibility calculations and From white paper to research plan.