Spatial quantum optical fluctuations are studied because of new potential applications of quantum optical procedures in parallel processing and multi-channel operation. The process of parametric down-conversion (PDC) is particularly suitable for the study of spatial effects, because of its large emission bandwidth in the spatial frequency domain. Recent theoretical investigations done for an arbitrary gain [1] have predicted multi-mode spatial correlations below shot-noise between several portions of the signal and idler emission cones that correspond to phase conjugate modes, when the size of the detection area in the far field is of the same order or larger than the coherence area of the radiation. Here we report on the first quantum spatial measurements of PDC radiation performed by using a 2 Hz-pulsed high-power laser (1GW-1ps) [2]. This enables us to tune the PDC to the high-gain regime while keeping a large pump beam size (∼1 mm). The huge number of transverse modes [roughly given by the ratio between i) the angular bandwidth of the PDC and ii) the inverse of the near field gain area] allows us to concentrate on a portion of the parametric fluorescence close to the collinear direction and within a narrow frequency bandwidth around degeneracy. This portion still contains a large (>1000) number of pairs of signal/idler correlated phase-conjugate modes, propagating at symmetrical directions with respect to the pump in order to fulfill the phase-matching constraints. The statistical ensemble averaging necessary for the quantum measurement is solely done over the spatial replicas (pairs of symmetrical spots) for each, single, pump-laser pulse. The single-shot measurements performed by means of a high efficiency CCD reveal sub-shot-noise spatial correlations for a PDC gain corresponding to the detection of up to 100 photoelectrons (pe) per mode. The observed transition from the quantum to the classical regime is attributed to a narrowing of the near-field gain profile that occurs at very high gain in presence of a bell-shaped pump beam, implying a broadening of the far-field coherence area. We therefore expect to go below shot-noise for higher gain by looking at correlation between groups of binned pixels. © 2005 IEEE.
Detection of quantum spatial correlation in high-gain parametric down-conversion
JEDRKIEWICZ, OTTAVIA;BRAMBILLA, ENRICO;BACHE, MORTEN;DI TRAPANI, PAOLO;
2005-01-01
Abstract
Spatial quantum optical fluctuations are studied because of new potential applications of quantum optical procedures in parallel processing and multi-channel operation. The process of parametric down-conversion (PDC) is particularly suitable for the study of spatial effects, because of its large emission bandwidth in the spatial frequency domain. Recent theoretical investigations done for an arbitrary gain [1] have predicted multi-mode spatial correlations below shot-noise between several portions of the signal and idler emission cones that correspond to phase conjugate modes, when the size of the detection area in the far field is of the same order or larger than the coherence area of the radiation. Here we report on the first quantum spatial measurements of PDC radiation performed by using a 2 Hz-pulsed high-power laser (1GW-1ps) [2]. This enables us to tune the PDC to the high-gain regime while keeping a large pump beam size (∼1 mm). The huge number of transverse modes [roughly given by the ratio between i) the angular bandwidth of the PDC and ii) the inverse of the near field gain area] allows us to concentrate on a portion of the parametric fluorescence close to the collinear direction and within a narrow frequency bandwidth around degeneracy. This portion still contains a large (>1000) number of pairs of signal/idler correlated phase-conjugate modes, propagating at symmetrical directions with respect to the pump in order to fulfill the phase-matching constraints. The statistical ensemble averaging necessary for the quantum measurement is solely done over the spatial replicas (pairs of symmetrical spots) for each, single, pump-laser pulse. The single-shot measurements performed by means of a high efficiency CCD reveal sub-shot-noise spatial correlations for a PDC gain corresponding to the detection of up to 100 photoelectrons (pe) per mode. The observed transition from the quantum to the classical regime is attributed to a narrowing of the near-field gain profile that occurs at very high gain in presence of a bell-shaped pump beam, implying a broadening of the far-field coherence area. We therefore expect to go below shot-noise for higher gain by looking at correlation between groups of binned pixels. © 2005 IEEE.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
