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A new scheme using macroscopic coherence is proposed from a theoretical point to experimentally determine the neutrino mass matrix, in particular the absolute value of neutrino masses, and the mass type, Majorana or Dirac. The proposed process is a collective, coherent Raman scattering followed by neutrino-pair emission from an excited state $|erangle$ of a long lifetime to a lower energy state $|grangle$; $gamma_0 + | erangle rightarrow gamma + sum_{ij} u_i bar{ u_j} + | grangle $ with $ u_i bar{ u_j}$ consisting of six massive neutrino-pairs. Calculated angular distribution has six $(ij)$ thresholds of massive neutrino-pair emission which show up as steps at different angles in the distribution. Angular locations of thresholds and event rates of the angular distribution make it possible to experimentally determine the smallest neutrino mass to the level of less than 1 meV (accordingly all three masses using neutrino oscillation data) , the mass ordering pattern , normal or inverted, and to distinguish whether neutrinos are of Majorana or Dirac type. Event rates of neutrino-pair emission, when the mechanism of macroscopic coherence amplification works, may become large enough for realistic experiments by carefully selecting certain types of target atoms or ions doped in crystals. The problem to be overcome is macro-coherently amplified quantum electrodynamic background of the process, $gamma_0 + | erangle rightarrow gamma +gamma_2 + gamma_3+ | grangle $, when two extra photons, $gamma_2,, gamma_3$, escape detection. We illustrate our idea using neutral Xe and trivalent Ho ion doped in dielectric crystals.
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Solid state quantum emitters have shown strong potential for applications in quantum information, but spectral inhomogeneity of these emitters poses a significant challenge. We address this issue in a cavity-quantum dot system by demonstrating cavity-stimulated Raman spin flip emission. This process avoids populating the excited state of the emitter and generates a photon that is Raman shifted from the laser and enhanced by the cavity. The emission is spectrally narrow and tunable over a range of at least 125 GHz, which is two orders of magnitude greater than the natural linewidth. We obtain the regime in which the Raman emission is spin-dependent, which couples the photon to a long-lived electron spin qubit. This process can enable an efficient, tunable source of indistinguishable photons and deterministic entanglement of distant spin qubits in a photonic crystal quantum network.
A new, indirect detection method of neutrino pairs $ ubar{ u}$ using magnetization generated at triggered radiative emission of neutrino pair (RENP), $ |e rangle rightarrow | g rangle + gamma + u bar{ u} $ (atomic de-transition from state $|e rangle $ to state $|g rangle$ accompanied by a photon $gamma$), is investigated in order to determine unknown neutrino properties; Majorana/Dirac distinction and absolute neutrino masses. Magnetization associated with RENP events has parity violating component intrinsic to weak interaction enforced by crystal field effect in solids, and greatly helps background rejection of quantum electrodynamic (QED) origin even when these backgrounds are amplified. In proposed experiment we prepare a coherently excited body of trivalent lanthanoid ions, Er$^{3+}$ (a best candidate ion so far found), doped in a transparent dielectric crystal. The magnetic moment $mu langle vec{S}cdotvec{k} rangle/k $ arising from generated electron spin $vec{S}$ parallel to trigger photon direction $vec{k}/k$ is parity odd, and is absent in QED processes. The generated magnetic field of order nano gauss or larger is stored in crystals long after pair emission event till spin relaxation time. An improved calculation method of coherent rate and angular distribution of magnetization is developed in order to incorporate finite size effect of crystal target beyond the infinite size limit in previous calculations.
A scheme of quantum electrodynamic (QED) background-free radiative emission of neutrino pair (RENP) is proposed in order to achieve precision determination of neutrino properties so far not accessible. The important point for the background rejection is the fact that the dispersion relation between wave vector along propagating direction in wave guide (and in a photonic-crystal type fiber) and frequency is modified by a discretized non-vanishing effective mass. This effective mass acts as a cutoff of allowed frequencies, and one may select the RENP photon energy region free of all macro-coherently amplified QED processes by choosing the cutoff larger than the mass of neutrinos.
Recent experiment proposed to observe induced radiative neutrino transitions are confronted to existing bounds on neutrino magnetic moments from earth-based experiments. These are found to exclude any observation by several orders of magnitude, unless the magnetic moments are assumed to be strongly momentum dependent. This possibility is discussed in some generality, and we find that nontrivial dependence of the neutrino form factor may indeed occur, leading to quite unexpected effects, although this is insufficient by orders of magnitude to justify the experiments.
We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e. by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs.
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