There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

All our former experience with application of quantum theory seems to say:
{\it what is predicted by quantum formalism must occur in laboratory} But the
essence of quantum formalism - entanglement, recognized by Einstein, Podolsky,
Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a
new resource as real as energy This holistic property of compound quantum systems, which involves
nonclassical correlations between subsystems, is a potential for many quantum
processes, including ``canonical'' ones: quantum cryptography, quantum
teleportation and dense coding However, it appeared that this new resource is
very complex and difficult to detect Being usually fragile to environment, it
is robust against conceptual and mathematical tools, the task of which is to
decipher its rich structure This article reviews basic aspects of entanglement including its
characterization, detection, distillation and quantifying In particular, the
authors discuss various manifestations of entanglement via Bell inequalities,
entropic inequalities, entanglement witnesses, quantum cryptography and point
out some interrelations They also discuss a basic role of entanglement in
quantum communication within distant labs paradigm and stress some
peculiarities such as irreversibility of entanglement manipulations including
its extremal form - bound entanglement phenomenon A basic role of entanglement
witnesses in detection of entanglement is emphasized

Quantum entanglement

Quantum networks provide opportunities and challenges across a range of intellectual and technical frontiers, including quantum computation, communication and metrology. The realization of quantum networks composed of many nodes and channels requires new scientific capabilities for generating and characterizing quantum coherence and entanglement. Fundamental to this endeavour are quantum interconnects, which convert quantum states from one physical system to those of another in a reversible manner. Such quantum connectivity in networks can be achieved by the optical interactions of single photons and atoms, allowing the distribution of entanglement across the network and the teleportation of quantum states between nodes.

The quantum internet

A single Ba/sup +/ ion is confined in a miniature Paul trap and Doppler cooled with green laser light at 493 nm and red light at 650 nm. A theoretical description of the experiment predicts that a level shift of the upper (P/sub 1/2/) state is associated with the modified decay. This level shift is observed in the following way: as the frequency detuning of the red laser is scanned across resonance, the phase between green and red fringes is recorded. Varying the mirror-ion distance leads to high-visibility interference fringes in the green fluorescence (/spl sim/60%) whilst the red fluorescence, that is transmitted by the mirror and detected by photomultiplier, is seen to be modulated with the same period but with lower visibility (/spl sim/1-2%). The modulation of the red light indicates a modified decay rate on the green transition, showing that the mirror changes the vacuum field at the green wavelength and leads to enhancement and inhibition of spontaneous decay from the upper state.

/pdf/vacuum-field-level-shifts-in-a-single-atom-mediated-by-a-2whuh0owcs.pdf

Vacuum-field level shifts in a single atom mediated by a single distant mirror

We propose a new protocol to implement ultra-fast two-qubit phase gates with trapped ions using spin-dependent kicks induced by resonant transitions By only optimizing the allocation of the arrival times in a pulse train sequence the gate is implemented in times faster than the trapping oscillation period $T<2\pi/\omega$ Such gates allow us to increase the number of gate operations that can be completed within the coherence time of the ion-qubits favoring the development of scalable quantum computers

Ultra-fast two-qubit ion gate using sequences of resonant pulses

The efficiency with which the position of a levitated nanoparticle is detected is one factor that sets the minimum temperature of the particle’s center-of-mass motion that can be achieved by feedback cooling. Typically, the detection is based on the interference of the light scattered by the particle with a reference Gaussian beam in a homodyne setup [1] - [3] . This detection scheme is limited by the wavefront mismatch between the scattered and the reference fields and by the numerical aperture (NA) of the lens that collects the scattered light. As a result of these limitations, temperatures close to the ground state have only been achieved in experiments exploiting high NA objectives (> 0.8), namely, optical-tweezer-based experiments [1] , [2] . Here, we demonstrate how the detection efficiency can be improved in a setup based on homodyne detection, by improving the mode-matching conditions and by increasing the sensitivity of the interference pattern to the displacement of the particle.

Detection of a Levitated Nanoparticle’s Position via Self-Homodyne

Laser-ion interactions that collectively couple the pseudo-spins of a string of trapped ions to one of the string's vibrational modes [1] have been used by us to entangle a pair of 40Ca+ ions with very high fidelity [2–4]. In addition, we experimentally confirmed that this gate mechanism allows for entangling ions without having recourse to ground state cooling [3]. This opens the way to performing an entangling gate after having applied an operation which does not preserve the ions' motional state like for example state detection.

Rainer Blatt

Papers

Vacuum-field level shifts in a single atom mediated by a single distant mirror

Ultra-fast two-qubit ion gate using sequences of resonant pulses

Detection of a Levitated Nanoparticle’s Position via Self-Homodyne

Entangling two and more ions with collective laser-ion interactions

High efficiency frequency doubled diode laser for precision spectroscopy of Single Ba* ions at 493 nm