Experimental observations of `quantum jumps' suggest that one can associate a timescale shorter than `lifetime' with quantum transitions; one such `jump time' is proposed here. We also find that experimental temporal localization of the jump does affect it (a lá Bohr), and predict an `observational line broadening'.
Experimental observations of quantum jumps' suggest that one can associate a timescale shorter than lifetime' with quantum transitions; one such jump time' is proposed here. We also find that experimental temporal localization of the jump does affect it (a lá Bohr), and predict an observational line broadening'.
Under unitary evolution, systems move gradually from state to state. An unstable atom has amplitude in its original state after many lifetimes (τL). But in the laboratory, transitions seem to go instantaneously, as suggested by the term "quantum jump." The problem studied here is whether the "jump" can be assigned a duration, in theory and in experiment. Two characteristic times are defined, jump time (τJ) and passage time (τP). Both use Zeno time, τZ, defined in terms of H and its initial state as τZ≡ℏ/, with $E_ψ\equiv $. τJ is defined in terms of the time needed to slow (à la the quantum Zeno effect) the decay: τJ≡τZ2/τL. It appears in several contexts. It is related to tunneling time in barrier penetration. Its inverse is the bandwidth of the Hamiltonian, in a time-energy uncertainty principle. τJ is also an indicator of the duration of the quadratic decay regime in both experiment and in numerical calculations (cf. Fig.~2 of PRA 57,1509 (1998).) The passage time, τP, arises from unitary evolution sans interpretation. It is based on a bound of Fleming (Nuov. Cim. 16 A, 232 (1973)): for any H and ψ a system cannot evolve to a state orthogonal to ψ for t<τP≡πτZ/2. By including apparatus in H, τP limits the observation of decay according to the quantum measurement ideas proposed in "Time's Arrows and Quantum Measurement," Cambridge U. Press, 1997, thereby allowing an experimental test of these ideas.
Recent experiments have found abrupt changes in the intensity of laser light scattered off single ions and atoms. These abrupt changes have been interpreted as resulting from Bohr's ``quantum jumps'' of the ion or atom from one state to another. In Bohr's description, such quantum jumps are not predicted by the Schr\"odinger equation and are introduced by additional postulates into quantum theory. We consider here an alternative explanation of these experiments using only properties of solutions of the Schr\"odinger equation and avoiding Bohr's added postulate.
We have recorded the laser-excited resonance fluorescence of one to three Ba+ ions and observed Bohr's "quantum jumps" when an ion decayed to the metastable 2D25 state, suddenly quenching its fluorescence. Most of the jumps mark Raman-Stokes scattering from the 2S21 and 2D23 levels.
Introduction The quantum theory of atoms and molecules had its origin in the famous 1913 paper of Bohr [186] in which he suggested that the interaction of radiation and atoms occurred with the transition of an atom from one stationary internal state to another, accompanied by the emission or absorption of radiation of a frequency determined by the energy difference between these states. These transitions came to be known as ‘quantum jumps’. Since all experiments until the late 1970s used to be carried out with large ensembles of atoms and molecules, these jumps were masked and could not be directly observed; they were only inferred from spectroscopic data. In fact, with the advent of quantum mechanics they eventually came to be regarded as artefacts of Bohr's simple-minded semi-classical model. But with the availability of coherent light sources and single ions prepared in ion traps [187], [188], and optically cooled [189], [190], the issue has been reopened with the experimental demonstration of quantum jumps in single ions [191], [192], [193]. These experiments have also opened up the contentious issue of wave function collapse or reduction on measurement, as they can be regarded as making collapse visible on the oscilloscope screen [191]. Evidence of the discrete nature of quantum transitions in a single quantum system had been accumulating from the observation of photon anti-bunching in single-atom resonance fluorescence [194], the tunneling of single electrons in metal–oxide-–semiconductor junctions [195] and spin-flips of individual electrons in a Penning trap [196].
According to the usual quantum description, the time evolution of the quantum state is continuous and deterministic except when a discontinuous and indeterministic collapse of state vector occurs. The collapse has been a central topic since the origin of the theory, although there are remarkable theoretical proposals to understand its nature, such as the Ghirardi–Rimini–Weber. Another possibility could be the assimilation of collapse with the now experimentally well established phenomenon of quantum jump, postulated by Bohr already in 1913. The challenge of nonlocality offers an opportunity to reconsider the quantum jump as a fundamental element of the logic of the physical world, rather than a subsidiary accident. We propose here a simple preliminary model that considers quantum jumps as processes of entry to and exit from the usual temporal domain to a timeless vacuum, without contradicting the quantum relativistic formalism, and we present some potential connections with particle physics. Quanta 2015; 4: 10–26.