QubitThe basic unit of quantum information, analogous to a classical bit but capable of existing in a superposition of 0 and 1 simultaneously.
SuperpositionA fundamental quantum principle where a quantum system exists in multiple states simultaneously until measured, enabling quantum sensors to probe multiple values at once.
EntanglementA quantum correlation between two or more particles where measuring one instantly determines the state of the other, regardless of distance, enabling enhanced measurement precision.
DecoherenceThe loss of quantum behavior due to interaction with the environment, which degrades the sensitivity advantage of quantum sensors and limits measurement time.
SQUIDSuperconducting Quantum Interference Device -- an extremely sensitive magnetometer that uses Josephson junctions in a superconducting loop to detect tiny magnetic flux changes.
NV CenterNitrogen-Vacancy center -- a point defect in diamond consisting of a nitrogen atom next to a lattice vacancy, whose spin state is sensitive to magnetic fields, temperature, and strain.
Josephson JunctionA thin insulating barrier between two superconductors through which Cooper pairs can tunnel, forming the basis of SQUID sensors and other superconducting quantum devices.
Heisenberg LimitThe fundamental quantum limit on measurement precision, scaling as 1/N where N is the number of quantum resources used, achievable through entanglement.
Shot Noise LimitThe classical limit on measurement precision arising from the discrete nature of particles (photons, atoms), scaling as 1/sqrt(N).
FemtoteslaA unit of magnetic field strength equal to 10^-15 Tesla, roughly the scale of magnetic fields produced by brain neural activity.
MagnetoencephalographyA neuroimaging technique that measures the magnetic fields produced by electrical activity in the brain, typically using SQUID sensors.
Coherence TimeThe duration over which a quantum system maintains its quantum properties before decoherence destroys them, a critical parameter for quantum sensor performance.
Ramsey InterferometryA technique for precise frequency and phase measurements using two separated interactions with an oscillating field, widely used in atomic clocks and quantum sensors.
Optical Lattice ClockAn atomic clock that traps atoms in a standing wave of laser light and probes an optical transition, achieving unprecedented timekeeping accuracy.
Quantum SqueezingA technique that reduces noise in one measurement variable below the standard quantum limit at the expense of increased noise in the conjugate variable, enhancing sensor sensitivity.
Zeeman EffectThe splitting of atomic energy levels in the presence of an external magnetic field, exploited by quantum magnetometers to measure magnetic field strength with extreme precision.
Spin-EchoA pulse sequence technique that reverses dephasing of quantum spins, extending effective coherence time and improving the sensitivity of NV center and atomic magnetometers.
Quantum Fisher InformationA measure of the information that a quantum state carries about an unknown parameter, setting the ultimate bound on measurement precision achievable by any quantum estimation strategy.
Atom InterferometryA technique that uses the wave-like properties of atoms to make precision measurements of gravity, rotation, and acceleration, forming the basis of quantum gravimeters and gyroscopes.
Magnetic Flux QuantumThe quantized unit of magnetic flux (Phi_0 = h/2e ≈ 2.07 x 10^-15 Wb), the fundamental quantity measured by SQUID sensors through flux quantization in superconducting loops.
Dynamic DecouplingA family of pulse sequences applied to quantum sensors that suppress environmental noise and extend coherence times, dramatically improving measurement sensitivity in real-world conditions.
Quantum GravimeterA device that uses atom interferometry or other quantum techniques to measure gravitational acceleration with extreme precision, useful for underground mapping and geodesy.
Standard Quantum LimitThe fundamental precision limit for measurements using uncorrelated (classical) quantum resources, corresponding to shot noise scaling as 1/sqrt(N) for N particles.
Quantum IlluminationA sensing protocol using entangled photons to detect targets in high-noise environments, achieving up to 6 dB advantage over classical methods in the low-signal regime.
MagnetocardiographyA non-invasive technique that measures the magnetic fields produced by electrical activity in the heart using SQUID or optically pumped magnetometer sensors.
Magic WavelengthA specific laser wavelength at which the differential light shift on the clock transition vanishes, enabling perturbation-free trapping in optical lattice clocks, invented by Hidetoshi Katori.