Entanglement of internal and external angular momenta of a single atom

We consider the exchange of spin and orbital angular momenta between a circularly polarized Laguerre-Gaussian beam of light and a single atom trapped in a two-dimensional harmonic potential. The radiation field is treated classically but the atomic center-of-mass motion is quantized. The spin and orbital angular momenta of the field are individually conserved upon absorption, and this results in the entanglement of the internal and external degrees of freedom of the atom. We suggest applications of this entanglement in quantum information processing.Comment: 4 pages, 2 figure

Predictors of malignancy in pancreatic head mass: a prospective study

A prospective study of patients presented with pancreatic head mass was conducted in a tertiary care referral hospital, Manipal, India from May 2006 to November 2008. The study population was divided into malignant and benign groups based on the final histopathology report. A univariate and multivariate analysis of potential predictive factors for malignancy were conducted. Results: A total of 102 patients with pancreatic head mass were included in the study after fulfilling the inclusion/exclusion criteria. 78 were malignant and 24 were benign. There was significant weight loss (p<0.001) and high mean bilirubin levels (p=0.002) in the malignant group. Mean CA 19-9 was significantly higher in the malignant group (290.7 vs. 30.3 U/ml; p<0.001). Sensitivity and specificity of CA 19-9 for detecting malignancy in pancreatic head mass at a cut off of 35U/ml was 86% and 79% respectively. CA 19-9 positivity rate was higher with increasing cut off values of 100, 200 and 300U/ml but such high levels occurred in fewer patients. All the non-jaundiced patients (100%) with raised CA 19-9 levels were found to be malignant compared to 86% malignancy in jaundiced patients. In multivariate analysis, a combination of weight loss > 10% of body weight and bilirubin > 3 mg/dl and CA 19-9 > 35U/ml had specificity and positive predictive value of 100% for predicting malignancy in pancreatic head mass. Conclusion: The presence of weight loss and jaundice and raised CA 19-9 levels together in a patient with pancreatic head mass can be predictive of malignancy. A very high CA 19-9 level can be an indicator of malignancy in a pancreatic head mass. A raised CA 19-9 level may be more predictive of malignancy in non-jaundiced patients than in jaundiced patients.Key words: Pancreatic Carcinoma, CA 19-9 Antige

Multi-valued Logic Gates for Quantum Computation

We develop a multi-valued logic for quantum computing for use in multi-level quantum systems, and discuss the practical advantages of this approach for scaling up a quantum computer. Generalizing the methods of binary quantum logic, we establish that arbitrary unitary operations on any number of d-level systems (d > 2) can be decomposed into logic gates that operate on only two systems at a time. We show that such multi-valued logic gates are experimentally feasible in the context of the linear ion trap scheme for quantum computing. By using d levels in each ion in this scheme, we reduce the number of ions needed for a computation by a factor of log d.Comment: Revised version; 8 pages, 3 figures; to appear in Physical Review

Inducing disallowed two-atom transitions with temporally entangled photons

Two uncoupled two-level atoms cannot be jointly excited by classical light under general circumstances, due to destructive interference of excitation pathways in two-photon absorption. However, with temporally entangled light, two-atom excitation is shown possible. Photons arising from three-level cascade decay are intrinsically ordered in time of emission. This field correlation induces a joint resonance in the two-atom excitation probability via suppression of one of the time-ordered excitation pathways. The relative gain in two-photon absorption increases with the time-frequency entanglement.Peer reviewedPhysic

Quantum information and computing in multilevel systems

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2002.We have studied the extension of the new field of quantum computing to the multilevel domain, where the information is stored in a coherent superposition of more than two levels. Interference and entanglement, the hallmarks of quantum mechanics, are more strikingly present in a multilevel system, in the form of wave packets and decoherence. This thesis explores new tools and applications for multilevel quantum information processing in Rydberg atoms. The quantum equivalent of a classical bit is a qubit, a two-level system. Quantum computational logic involves conditional unitary transforms on two qubits, which are the quantum analogs of logic gates in classical computer science. The multilevel extension of a qubit is a qudit, a d-level quantum system. We present several programs for universal quantum logic involving qudits, and physically motivate the formalism with examples from quantum control. Wave packets arise from multilevel quantum interference, and they give an interesting new perspective on quantum information stored in a multilevel system. We show that an alternative realization of a qudit in a quantum system is a set of d wave-packet states that are physically separated in time. The wavepacket basis is connected to the energy-level basis by a Fourier transform, a key ingredient of quantum algorithms. We apply these ideas to Rydberg atoms, and show that an appropriate coupling between such atoms enables a conceptually simpler implementation of the quantum version of the Fast Fourier transform algorithm. Lastly we explore atomic angular momentum as a computational observable. Most of the states in the hydrogen atom are degenerate in energy but differ by discrete units of angular momentum. We show that using Laguerre-Gaussian laser modes, which possess orbital field angular momentum, these internal angular momentum states in the atom can be entangled with its quantized center-of-mass angular momentum. We propose this entanglement as the building block for multilevel quantum computing using angular-momentum states