RESUMEN
We report on simulations of the degree of polarization entanglement of photon pairs simultaneously emitted from a quantum dot-cavity system that demand revisiting the role of phonons. Since coherence is a fundamental precondition for entanglement and phonons are known to be a major source of decoherence, it seems unavoidable that phonons can only degrade entanglement. In contrast, we demonstrate that phonons can cause a degree of entanglement that even surpasses the corresponding value for the phonon-free case. In particular, we consider the situation of comparatively small biexciton binding energies and either finite exciton or cavity mode splitting. In both cases, combinations of the splitting and the dot-cavity coupling strength are found where the entanglement exhibits a nonmonotonic temperature dependence which enables entanglement above the phonon-free level in a finite parameter range. This unusual behavior can be explained by phonon-induced renormalizations of the dot-cavity coupling g in combination with a nonmonotonic dependence of the entanglement on g that is present already without phonons.
RESUMEN
We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations.
RESUMEN
It is demonstrated how the exciton and the biexciton state of a quantum dot can be prepared with high fidelity on a picosecond time scale by driving the dot with a strong laser pulse that is tuned above the exciton resonance for exciton preparation and in resonance with the exciton transition for biexciton preparation. The proposed protocols make use of the phonon-induced relaxation towards photon dressed states in optically driven quantum dots and combine the simplicity of traditional Rabi oscillation schemes with the robustness of adiabatic rapid passage schemes. Our protocols allow for an on-demand, fast, and almost perfect state preparation even at strong carrier-phonon interaction where other schemes fail. In fact, the performance of the presented protocols is shown to be better the stronger the carrier-phonon interaction is.
RESUMEN
BACKGROUND: The relatively low incidence (6 to 31 percent) of axillary metastasis in patients with T1 carcinoma of the breast (20 mm or smaller) has led some surgeons to question routine axillary lymphadenectomy (ALND) for patients with no palpable axillary metastases and T1 tumors. This study was undertaken to determine the incidence and predictors of axillary lymph node metastasis in patients with T1 carcinoma of the breast and evaluate the role of sentinel lymphadenectomy (SLND) in this context. STUDY DESIGN: All patients with T1 invasive carcinoma of the breast treated at the John Wayne Cancer Institute between January 1988 and June 1994 were prospectively studied. The study population was comprised of 259 women who had ALND. Of these patients, 114 were part of a pilot study examining the efficacy of SLND. RESULTS: Of the 259 women, 69 (27 percent) had axillary metastasis. Hematoxylin and eosin staining identified nodal involvement in 13 percent of patients with T1a and T1b tumors (10 mm or less) and in 30 percent of patients with T1c tumors (p = 0.002). Other factors such as age, hormone receptor status, presence of ductal carcinoma in situ, histology, ploidy, and S-phase were not significant predictors of involvement. A sentinel node was identified in 73 patients: this node accurately predicted axillary status in 72 patients, was the only positive node in nine of 16 patients with axillary involvement, and was 100 percent predictive of axillary status when the primary tumor was 10 mm or less. Retrospective immunohistochemical staining revealed an additional seven patients with positive sentinel nodes. With this technique, even T1a lesions had a 15 percent incidence of axillary metastasis. CONCLUSIONS: Tumor size is the only accurate predictor of axillary metastasis in patients with T1 carcinoma of the breast. The significant incidence of axillary involvement from T1 tumors mandates accurate staging, even when the tumor is 10 mm or less in size. Examination of a sentinel lymph node may accurately predict axillary metastasis.