Quantum noise
Quantum noise is noise arising from the indeterminate state of matter in accordance with fundamental principles of quantum mechanics, specifically the uncertainty principle and via zero-point energy fluctuations.In contrast to shot noise,[clarification needed] the quantum mechanical uncertainty principle sets a lower limit to a measurement.In general, noise is uncontrolled random variation from an expected value and is typically unwanted.In astronomy, a device which pushes against the limits of quantum noise is the LIGO gravitational wave observatory.Quantum noise can be illustrated by considering a Heisenberg microscope where an atom's position is measured from the scattering of photons.The precision of the position measurement can be increased at the expense of knowing the atom's momentum.First, it will impart momentum back onto the measuring devices in extreme cases.Precise and sensitive instrumentation will approach the uncertainty principle at sufficiently control environments.which measures when our signal is positively, negatively or not correlated at different timesThe Wiener–Khinchin theorem generally states that a noise's power spectrum is given as the autocorrelation of a signal, i.e.,In the above outline, we assumed that One can show that an ideal "top-hat" signal, which may correspond to a finite measurement of a voltage over some time, will produce noise across its entire spectrum as a sinc function.are the quantum statistical average using the density matrix in the Heisenberg picture.Typically, the positive frequency of the spectral density corresponds to the flow of energy into the oscillator (for example, the photons' quantized field), while the negative frequency corresponds to the emitted of energy from the oscillator.Physically, an asymmetric spectral density would correspond to either the net flow of energy from or to our oscillator model.[6] Consider the amplification of stream of photons, an ideal linear noiseless gain, and the Energy-Time uncertainty relation.We also assume a unity quantum efficiency, or every photon is converted to a photocurrent.A deeper analysis done by H. Heffner showed the minimum noise power output required to meet the Heisenberg uncertainty principle is given as[7]In an electric circuit, the random fluctuations of a signal due to the discrete character of electrons can be called quantum noise.Generally speaking, they amplified a Nd:YAG free space laser with minimal noise addition as it transitioned from linear to nonlinear amplification.The experiment required Fabry-Perot for filtering laser mode noises and selecting frequencies, two separate but identical probe and saturating beams to ensure uncorrelated beams, a zigzag slab gain medium, and a balanced detector for measuring quantum noise or shot-noise limited noise.corresponds to the emission cross section and upper population number productas the photons travel through a medium of excited and ground state atoms from positionThe existence of zero-point energy fluctuations is well-established in the theory of the quantised electromagnetic field.This vacuum fluctuation or quantum noise will effect classical systems.[clarification needed] Because entanglement is studied intensely in simple pairs of entangled photons, for example, decoherence observed in experiments could well be synonymous with "quantum noise" as to the source of the decoherence.Vacuum fluctuation is a possible causes for a quanta of energy to spontaneously appear in a given field or spacetime, then thermal differences must be associated with this event.[dubious – discuss] A laser is described by the coherent state of light, or the superposition of harmonic oscillators eigenstates.[12] The laser is a quantum mechanical phenomena (see Maxwell–Bloch equations, rotating wave approximation, and semi-classical model of a two level atom).The Einstein coefficients and the laser rate equations are adequate if one is interested in the population levels and one does not need to account for population quantum coherences (the off diagonal terms in a density matrix).The relative error of measurement of the intensity due to the quantum noise is on the order of 10−5.