Deterministic secure quantum communication with and without entanglement

We present a protocol for sending a message over a quantum channel with different layers of security that will prevent an eavesdropper from deciphering the message without being detected. The protocol has two versions where the bits are encoded in either pairs of entangled photons or separate photons. Unlike many other protocols, it requires a one-way, rather than a two-way, quantum channel and does not require a quantum memor. A quantum key is used to encrypt the message and both the key and the message are sent over the quantum channle with the same quantum encoding technique. The key is sent only if no eavesdropper is detected.Comment: 9 pages, 3 figures. Major changes in section 3 and 4. Accepted for publication in Physica Script

Interpreting Recoil For Undergraduate Students

In this paper, I outline some problems in the students' understanding of the explanation of recoil motion when introduced to them in the context of Newton's third law. I propose to explain the origin of recoil from a microscopic point of view, which emphasizes the exact mechanism leading to recoil. This mechanism differs from one system to another. Several examples that can be easily implemented in the classroom environment are given in this paper. Such a profound understanding of the origin of recoil help students avoid some of the misconceptions that might arise from the phenomenological approach, and stimulates their thinking in the fundamental origins of other physical phenomena.Comment: To Appear in The Physics Teacher Magazin

Quantum key distribution based on the quantum eraser

Quantum information and quantum foundations are becoming popular topics for advanced undergraduate courses. Many of the fundamental concepts and applications in these two fields, such as delayed choice experiments and quantum encryption, are comprehensible to undergraduates with basic knowledge of quantum mechanics. In this paper, we show that the quantum eraser, usually used to study the duality between wave and particle properties, can also serve as a generic platform for quantum key distribution. We present a pedagogical example of an algorithm to securely share random keys using the quantum eraser platform and propose its implementation with quantum circuits.Comment: 7 pages, 4 figures; updated versio

Regression relation for pure quantum states and its implications for efficient computing

We obtain a modified version of the Onsager regression relation for the expectation values of quantum-mechanical operators in pure quantum states of isolated many-body quantum systems. We use the insights gained from this relation to show that high-temperature time correlation functions in many-body quantum systems can be controllably computed without complete diagonalization of the Hamiltonians, using instead the direct integration of the Schroedinger equation for randomly sampled pure states. This method is also applicable to quantum quenches and other situations describable by time-dependent many-body Hamiltonians. The method implies exponential reduction of the computer memory requirement in comparison with the complete diagonalization. We illustrate the method by numerically computing infinite-temperature correlation functions for translationally invariant Heisenberg chains of up to 29 spins 1/2. Thereby, we also test the spin diffusion hypothesis and find it in a satisfactory agreement with the numerical results. Both the derivation of the modified regression relation and the justification of the computational method are based on the notion of quantum typicality.Comment: 16 pages, 4 figures; minor textual corrections; parts rearrange

Cooling classical many-spin systems using feedback control

We propose a technique for polarizing and cooling finite many-body classical systems using feedback control. The technique requires the system to have one collective degree of freedom conserved by the internal dynamics. The fluctuations of other degrees of freedom are then converted into the growth of the conserved one. The proposal is validated using numerical simulations of classical spin systems in a setting representative of Nuclear Magnetic Resonance experiments. In particular, we were able to achieve 90 percent polarization for a lattice of 1000 classical spins starting from an unpolarized infinite temperature state

Chaos and Relaxation in Classical and Quantum Spin Systems

The problems of chaos and relaxation have a fundamental importance in the study of many-body classical and quantum systems. We investigate some of the issues related to these problems numerically in classical and quantum spin systems. New results reported in this thesis include: (i) A remarkably simple algorithm for discriminating chaotic from nonchaotic behavior in classical systems using a time series of one macroscopic observable. The effectiveness of this algorithm stems from the qualitative differences in the power spectra of chaotic and nonchaotic systems. (ii) A modified version of the Onsager regression relation applicable to pure quantum states. (iii) An efficient algorithm for computing the infinitetemperature time correlation functions in systems with large Hilbert spaces. (iv) Absence of exponential sensitivity to small perturbations in macroscopic nonintegrable systems of spins 1/2 . Such a behavior is contrasted with the exponential sensitivity to small perturbations in chaotic classical spin systems. (v) Accurate numerical investigations of free induction decay and spin diffusion in certain spin lattices. The consequences of these results have implications for the foundations of statistical mechanics or practical problems such as computing the long-time behavior of the free induction decay in solids

Risk factors of progression of chronic kidney disease patients under conservative treatment

Background: Chronic kidney disease (CKD) is recognized as a major health problem affecting approximately 13% of the US population. Early identification and treatment of risk factors of progression of chronic kidney disease can provide marked benefits later in the term of delaying progression to renal replacement therapy.Methods: The medical chart for 92 CKD patients on regular follow up in low clearance clinic with GFR below 20 ml/min were retrospectively reviewed annually for 4 years regular follow up period. The following variables were recorded for each patient: non-modifiable variables (Age, sex, nationality, BMI, systolic and diastolic blood pressure, smoking status, causes of kidney disease, diabetes status, hepatitis status, medication used (like ACEi/ARBs and Sodium bicarbonate) and modifiable variables which includes: Serum albumin, potassium level, serum bicarbonate level, level of proteinuria, rate of GFR decline (Delta GFR) /year, total cholesterol level and hemoglobin level. Then they were divided into 2 groups according to the endpoint during the follow up period. Group 1 include patients did not start dialysis yet and group 2 which include patients who started dialysis during their regular follow up period.Results: There is no statistically significant differences between the two groups regarding Age , sex, systolic and diastolic blood pressure and Body Mass Index( BMI), serum albumin and haemoglobin levels (p 0.295, 0.317, 0.220, 0.181,0.805, 0.884 and 0.451 respectively). There is no statistically a difference between the two groups regarding serum potassium level and serum total cholesterol level (p 0.515 and 0.517 respectively). Diabetic patients started dialysis earlier than non-diabetics with statistically significant difference between the two groups (p 0.029). The patients who weren’t taking ACEi or ARBs started dialysis earlier than those who were taking (p 0.005), while there was no significant differences between the two groups regarding sodium bicarbonate intake (p 0.256). Low sodium bicarbonate level and severity of proteinuria are of significantly important risk factors for progression of CKD disease (p 0.006 and 0.029 respectively).Conclusions: The most important risk factors for rapid progression are presence of diabetes, severity of proteinuria and low serum bicarbonate level in advanced stages of chronic kidney disease. Early recognition of these risk factors and their correction may retard the progression of CKD, which will delay the need for renal replacement therapy. In addition, ACEI or ARBs intake are almost renoprotective and may delay the rapid progression of chronic kidney disease especially in proteinuric patients.