Emergence of a measurement basis in atom-photon scattering

The process of quantum measurement has been a long standing source of debate. A measurement is postulated to collapse a wavefunction onto one of the states of a predetermined set - the measurement basis. This basis origin is not specified within quantum mechanics. According to the theory of decohernce, a measurement basis is singled out by the nature of coupling of a quantum system to its environment. Here we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion due to spontaneous photon scattering. Using quantum process tomography we visualize the projection of all spin directions, onto this basis, as a photon is scattered. These basis spin states are found to be aligned with the scattered photon propagation direction. In accordance with decohernce theory, they are subjected to a minimal increase in entropy due to the photon scattering, while, orthogonal states become fully mixed and their entropy is maximally increased. Moreover, we show that detection of the scattered photon polarization measures the spin state of the ion, in the emerging basis, with high fidelity. Lastly, we show that while photon scattering entangles all superpositions of pointer states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings show that photon scattering by atomic spin superpositions fulfils all the requirements from a quantum measurement process

Microflow of fluorescently labelled red blood cells in tumours expressing single isoforms of VEGF and their response to VEGF-R tyrosine kinase inhibition

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In this work we studied the functional differences between the microcirculation of murine tumours that only express single isoforms of vascular endothelial growth factor-A (VEGF), VEGF120 and VEGF188, and the effect of VEGF receptor tyrosine kinase (VEGF-R TK) inhibition on their functional response to the vascular disrupting agent, combretastatin A-4 phosphate (CA-4-P). We used measurement of fluorescentlylabelled red blood cell (RBC) velocities in tumour microvessels to study this functional response. RBC velocity for control VEGF120-expressing tumours was over 50% slower than for control VEGF188-expressing tumours, which may be due to the immature and haemorrhagic vasculature of the VEGF120 tumour. After chronic treatment with a VEGF-R tyrosine kinase inhibitor, SU5416, RBC velocities in VEGF120 tumours were significantly increased compared to control VEGF120 tumours, and similar to velocities in both VEGF188 treatment groups. Control and SU5416 treated VEGF188 tumours were not different from each other. Treatment of VEGF120 tumours with SU5416 reduced their vascular response to CA-4-P to a similar level to the VEGF188 tumours. Differential expression of VEGF isoforms not only affected vascular function in untreated tumours but also impacted on response to a vascular disrupting drug, CA-4-P, alone and in combination with an anti-angiogenic approach involving VEGF-R TK inhibition. Analysis of RBC velocities is a useful tool in measuring functional responses to vascular targeted treatments.This study is funded by the Cancer Research UK

Zero Field precession and hysteretic threshold currents in spin torque oscillators with tilted polarizer

Using non-linear system theory and numerical simulations we map out the static and dynamic phase diagram in zero applied field of a spin torque oscillator with a tilted polarizer (TP-STO).We find that for sufficiently large currents, even very small tilt angles (beta>1 degree) will lead to steady free layer precession in zero field. Within a rather large range of tilt angles, 1 degree< beta <19 degree, we find coexisting static states and hysteretic switching between these using only current. In a more narrow window (1 degree<beta<5 degree) one of the static states turns into a limit cycle (precession). The coexistence of static and dynamic states in zero magnetic field is unique to the tilted polarizer and leads to large hysteresis in the upper and lower threshold currents for TP-STO operation.Comment: 5 pages, 4 figure

Quantum control of 88^{88}Sr+^+ in a miniature linear Paul trap

We report on the construction and characterization of an apparatus for quantum information experiments using $^{88}$Sr$^+$ ions. A miniature linear radio-frequency (rf) Paul trap was designed and built. Trap frequencies above 1 MHz in all directions are obtained with 50 V on the trap end-caps and less than 1 W of rf power. We encode a quantum bit (qubit) in the two spin states of the $S_{1/2}$ electronic ground-state of the ion. We constructed all the necessary laser sources for laser cooling and full coherent manipulation of the ions' external and internal states. Oscillating magnetic fields are used for coherent spin rotations. High-fidelity readout as well as a coherence time of 2.5 ms are demonstrated. Following resolved sideband cooling the average axial vibrational quanta of a single trapped ion is $\bar n=0.05$ and a heating rate of $\dot{\bar n}=0.016$ ms$^{-1}$ is measured.Comment: 8 pages,9 figure

Measuring Red Blood Cell Velocity with a Keyhole Tracking Algorithm

A tracking algorithm is proposed to measure the velocity of red blood cells traveling through microvessels of tumors growing in skin flaps implanted on mice. The tracking is based on a keyhole model that describes the probable movement of a segmented cell between contiguous frames in a video sequence. When a history of movements exists, past, present and a predicted landing position define two regions of probability with a keyhole shape. This keyhole is used to de- termine if cells in contiguous frames should be linked to form tracks. Pre-processing segments cells from background and post-processing joins tracks and discards links that could have been formed due to noise or uncertainty. The algorithm pre- sents several advantages over traditional methods such as kymographs or particle image velocimetry: manual interven- tion is restricted to the thresholding, several vessels can be analyzed simultaneously, algorithm is robust to noise and a wealth of statistical measures can be obtained. Two tumors with different geometries were analyzed; average velocities were 211±136 [μm/s] (mean±std) with a range 15.9-797 [μm/s], and 89±62 [μm/s] with a range 5.5-300 [μm/s] respec- tively, which are consistent with previous results in the litera- ture

A scale-space tracing algorithm for analysis of tumour blood vessel morphology from transmitted light optical images

Background Limited contrast in optical images is problematic for analysing tumour vascular morphology. We describe an algorithm for segmenting tumour vasculature in transmitted light optical images, without the need for contrast enhancement. Effects of angiopoietin-1 (Ang-1) and -2 (Ang-2) ± treatment with the vascular disrupting agent combretastatin A4P (CA4P) were investigated. Method SW1222 human colorectal carcinoma cells were transfected with Ang-1 or Ang-2 cDNA, or with empty vector and implanted into ‘window’ chamber-bearing mice. Transmitted light images of tumours (x10 objective) were acquired before and up to 24h after treatment with 30 mg/kg CA4P or saline. Vessel tracing used a scale-space approach, employing differences in intensity of transmitted light between the vessels and surrounding tissues, as well as differences in the chromatic components, hue and saturation. The centreline of vessels was detected as a “ridge” in a topographical analogy and successive levels of filtering provided different scales to detect sharp to diffuse ridges. Morphological parameters were measured from the traced images - average vessel length (AL) width (AW), and relative vascular area (RA). Results The algorithm successfully identified the majority of tumour microvessels. CA4P-treated tumours showed a decrease in RA and increase in saturation balance up to 1-3h, with recovery by 24h. Saline had no effect. Ang-2 over-expressing tumours had lower values of AL, AW and RA than Ang-1 and wild-type (WT) tumours. Ang-1 tumours were similar to the WT except that AL was longer

Segmentation and morphological analysis of microvessels in immunostained histological tumour sections

Segmentation and morphological analysis of microvessels in immunostained histological tumour sectionsA fully automatic segmentation and morphological analysis algorithm for the analy- sis of microvessels from CD31 immunostained histological tumour sections is presented. The algorithm exploited the distinctive hues of stained vascular endothelial cells, cell nuclei and background, which provided the seeds for a region-growing algorithm in the 3D Hue, Saturation, Value (HSV) colour model. The segmented objects, identified as microvessels by CD31 immunostaining, were post-processed with three morphological tasks: joining separate objects that were likely to belong to a single vessel, closing ob- jects that had a narrow gap around their periphery, and splitting objects with multiple lumina into individual vessels