Noise and Measurement Efficiency of a Partially Coherent Mesoscopic Detector

We study the noise properties and efficiency of a mesoscopic resonant-level conductor which is used as a quantum detector, in the regime where transport through the level is only partially phase coherent. We contrast models in which detector incoherence arises from escape to a voltage probe, versus those in which it arises from a random time-dependent potential. Particular attention is paid to the back-action charge noise of the system. While the average detector current is similar in all models, we find that its noise properties and measurement efficiency are sensitive both to the degree of coherence and to the nature of the dephasing source. Detector incoherence prevents quantum limited detection, except in the non-generic case where the source of dephasing is not associated with extra unobserved information. This latter case can be realized in a version of the voltage probe model.Comment: 15 pages, 5 figures; revised dicussion of voltage probe model

Calorimetric readout of a superconducting proximity-effect thermometer

A proximity-effect thermometer measures the temperature dependent critical supercurrent in a long superconductor - normal metal - superconductor (SNS) Josephson junction. Typically, the transition from the superconducting to the normal state is detected by monitoring the appearance of a voltage across the junction. We describe a new approach to detect the transition based on the temperature increase in the resistive state due to Joule heating. Our method increases the sensitivity and is especially applicable for temperatures below about 300 mK.Comment: 10 pages, 5 figures. To appear in the proceedings of the Conference on Micro- and Nanocryogenics (LT25 satellite) organized in Espoo, Finland (2008

α,α-Difluoro-β-ketophosphonates on a tetraazamacrocyclic platform: Synthesis and inhibitory activity against protein tyrosine phosphatases

The present study offers a new approach for designing inhibitors of protein tyrosine phosphatases. We have synthesized the cyclam derivatives with α,α-difluoro-β-ketophosphonate fragments covalently attached to tetraazamacrocyclic scaffold, which is known to be of medical interest. The obtained functionalized macrocycles were evaluated as inhibitors of PTP1B, TC-PTP, CD45, and other protein tyrosine phosphatases.Запроновано новий пiдхiд до розробки iнгiбiторiв протеїнтирозинфосфатаз. Синтезовано похiднi цикламу з α,α-дифторо-β-кетофосфонатними фрагментами, ковалентно зв’язаними з тетраазамакроциклiчною платформою. Отриманi функцiоналiзованi макроцикли було дослiджено як iнгiбiтори PTP1B, TC-PTP, CD45 та iнших протеїнтирозинфосфатаз.Предложен новый поход к разработке ингибиторов протеинтирозинфосфатаз. Синтезированы производные циклама с α,α-дифтор-β-кетофосфонатными фрагментами, ковалентно связанными с тетраазамакроциклической платформой. Полученные функционализированные макроциклы были изучены в качестве ингибиторов PTP1B, TC-PTP, CD45 и других протеинтирозинфосфатаз

Quantum information processing with superconducting qubits in a microwave field

We investigate the quantum dynamics of a Cooper-pair box with a superconducting loop in the presence of a nonclassical microwave field. We demonstrate the existence of Rabi oscillations for both single- and multi-photon processes and, moreover, we propose a new quantum computing scheme (including one-bit and conditional two-bit gates) based on Josephson qubits coupled through microwaves.Comment: 7 pages, 1 figur

Fast noise in the Landau-Zener theory

We study the influence of a fast noise on Landau-Zener transitions. We demonstrate that a fast colored noise much weaker than the conventional white noise can produce transitions itself or can change substantially the Landau-Zener transition probabilities. In the limit of fast colored or strong white noise we derive asymptotically exact formulae for transition probabilities and study the time evolution of a spin coupled to the noise and a sweeping magnetic field.Comment: 28 pages, 5 figure

Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from [email protected], submitted to Phys.Rev.

Green function techniques in the treatment of quantum transport at the molecular scale

The theoretical investigation of charge (and spin) transport at nanometer length scales requires the use of advanced and powerful techniques able to deal with the dynamical properties of the relevant physical systems, to explicitly include out-of-equilibrium situations typical for electrical/heat transport as well as to take into account interaction effects in a systematic way. Equilibrium Green function techniques and their extension to non-equilibrium situations via the Keldysh formalism build one of the pillars of current state-of-the-art approaches to quantum transport which have been implemented in both model Hamiltonian formulations and first-principle methodologies. We offer a tutorial overview of the applications of Green functions to deal with some fundamental aspects of charge transport at the nanoscale, mainly focusing on applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references, submitted to Springer series "Lecture Notes in Physics

α,α-Difluoro-β-ketophosphonates on a tetraazamacrocyclic platform: Synthesis and inhibitory activity against protein tyrosine phosphatases

The present study offers a new approach for designing inhibitors of protein tyrosine phosphatases. We have synthesized the cyclam derivatives with α,α-difluoro-β-ketophosphonate fragments covalently attached to tetraazamacrocyclic scaffold, which is known to be of medical interest. The obtained functionalized macrocycles were evaluated as inhibitors of PTP1B, TC-PTP, CD45, and other protein tyrosine phosphatases.Запроновано новий пiдхiд до розробки iнгiбiторiв протеїнтирозинфосфатаз. Синтезовано похiднi цикламу з α,α-дифторо-β-кетофосфонатними фрагментами, ковалентно зв’язаними з тетраазамакроциклiчною платформою. Отриманi функцiоналiзованi макроцикли було дослiджено як iнгiбiтори PTP1B, TC-PTP, CD45 та iнших протеїнтирозинфосфатаз.Предложен новый поход к разработке ингибиторов протеинтирозинфосфатаз. Синтезированы производные циклама с α,α-дифтор-β-кетофосфонатными фрагментами, ковалентно связанными с тетраазамакроциклической платформой. Полученные функционализированные макроциклы были изучены в качестве ингибиторов PTP1B, TC-PTP, CD45 и других протеинтирозинфосфатаз