Coherent control of Rydberg states in silicon.

Laser cooling and electromagnetic traps have led to a revolution in atomic physics, yielding dramatic discoveries ranging from Bose-Einstein condensation to the quantum control of single atoms. Of particular interest, because they can be used in the quantum control of one atom by another, are excited Rydberg states, where wavefunctions are expanded from their ground-state extents of less than 0.1 nm to several nanometres and even beyond; this allows atoms far enough apart to be non-interacting in their ground states to strongly interact in their excited states. For eventual application of such states, a solid-state implementation is very desirable. Here we demonstrate the coherent control of impurity wavefunctions in the most ubiquitous donor in a semiconductor, namely phosphorus-doped silicon. In our experiments, we use a free-electron laser to stimulate and observe photon echoes, the orbital analogue of the Hahn spin echo, and Rabi oscillations familiar from magnetic resonance spectroscopy. As well as extending atomic physicists' explorations of quantum phenomena to the solid state, our work adds coherent terahertz radiation, as a particularly precise regulator of orbitals in solids, to the list of controls, such as pressure and chemical composition, already familiar to materials scientists.

Neurosarcoidosis-related intracranial haemorrhage: three new cases and a systematic review of the literature.

BACKGROUND AND PURPOSE: Intracranial haemorrhage in neurosarcoidosis (NS-ICH) is rare, poorly understood and the diagnosis of NS may not be immediately apparent. METHODS: The clinical features of three new NS-ICH cases are described including new neuropathological findings and collated with cases from a systematic literature review. CASES: (i) A 41-year-old man with headaches, hypoandrogenism and encephalopathy developed a cerebellar haemorrhage. He had neuropathological confirmation of NS with biopsy-proven angiocentric granulomata and venous disruption. He responded to immunosuppressive therapy. (ii) A 41-year-old man with no history of hypertension was found unconscious. A subsequently fatal pontine haemorrhage was diagnosed. Liver biopsy revealed sarcoid granulomas. (iii) A 36-year-old man with raised intracranial pressure headaches presented with a seizure and a frontal haemorrhage. Hilar lymph node biopsy confirmed sarcoidosis, and he was treated successfully. Systematic review: Twelve other published cases were identified and collated with our cases. Average age was 36 years and M:F = 2.3:1; 46% presented with neurological symptoms and 31% had CNS-isolated disease. Immediate symptoms of ICH were acute/worsening headache or seizures (60%). ICH was supratentorial (62%), infratentorial (31%) or subarachnoid (7%). Forty percent had definite NS, 53% probable NS and 7% possible NS (Zajicek criteria). Antigranulomatous/immunosuppressive therapy regimens varied and 31% died. CONCLUSIONS: This series expands our knowledge of the pathology of NS-ICH, which may be of arterial or venous origin. One-third have isolated NS. Clinicians should consider NS in young-onset ICH because early aggressive antigranulomatous therapy may improve outcome.

Experimental determination of the Rashba coefficient in InSb/InAlSb quantum wells at zero magnetic field and elevated temperatures.

We report the optical measurement of the spin dynamics at elevated temperatures and in zero magnetic field for two types of degenerately doped n-InSb quantum wells (QWs), one asymmetric (sample A) and one symmetric (sample B) with regards to the electrostatic potential across the QW. Making use of three directly determined experimental parameters: the spin lifetime, τ(s), the sheet carrier concentration, n, and the electron mobility, µ, we directly extract the zero-field spin splitting. For the asymmetric sample where the Rashba interaction is the dominant source of spin splitting, we deduce a room temperature Rashba parameter of α = 0.09 ± 0.1 eV Å which is in good agreement with calculations and we estimate the Rashba coefficient α(0) (a figure of merit for the ease with which electron spins can be modulated via an electric field). We review the merits/limitations of this approach and the implications of our findings for spintronic devices.

The multi-photon induced Fano effect.

The ordinary Fano effect occurs in many-electron atoms and requires an autoionizing state. With such a state, photo-ionization may proceed via pathways that interfere, and the characteristic asymmetric resonance structures appear in the continuum. Here we demonstrate that Fano structure may also be induced without need of auto-ionization, by dressing the continuum with an ordinary bound state in any atom by a coupling laser. Using multi-photon processes gives complete, ultra-fast control over the interference. We show that a line-shape index q near unity (maximum asymmetry) may be produced in hydrogenic silicon donors with a relatively weak beam. Since the Fano lineshape has both constructive and destructive interference, the laser control opens the possibility of state-selective detection with enhancement on one side of resonance and invisibility on the other. We discuss a variety of atomic and molecular spectroscopies, and in the case of silicon donors we provide a calculation for a qubit readout application.

Age related outcome in acute subdural haematoma following traumatic head injury.

Acute subdural haematoma (ASDH) is one of the conditions most strongly associated with severe brain injury. Reports prior to 1980 describe overall mortality rates for acute subdural haematomas (SDH's) ranging from 40% to 90% with poor outcomes observed in all age groups. Recently, improved results have been reported with rapid diagnosis and surgical treatment. The elderly are predisposed to bleeding due to normal cerebral atrophy related to aging, stretching the bridging veins from the dura. Prognosis in ASDH is associated with age, time from injury to treatment, presence of pupillary abnormalities, Glasgow Coma Score (GCS) or motor score on admission, immediate coma or lucid interval, computerized tomography findings (haematoma volume, degree of midline shift, associated intradural lesion, compression of basal cisterns), post-operative intracranial pressure and type of surgery. Advancing age is known to be a determinant of outcome in head injury. We present the results of a retrospective study carried out in Beaumont Hospital, Dublin, Ireland's national neurosurgical centre. The aim of our study was to examine the impact of age on outcome in patients with ASDH following severe head injury. Only cases with acute subdural haematoma requiring surgical evacuation were recruited. Mortality was significantly higher in older patients (50% above 70 years, 25.6% between 40 and 70 years and 26% below 40 years). Overall poor outcome (defined as Glasgow outcome scores 3-5) was also higher in older patients; 74.1% above 70 years, 48% between 40 and 70 years and 30% below 40 years. Poor outcome in traumatic acute subdural haematoma is higher in elderly patients even after surgical intervention.

Spin preservation during THz orbital pumping of shallow donors in silicon.

We investigate the spin relaxation under conditions of optical excitation between the Rydberg orbital states of phosphorus donor impurities in silicon. Here we show that the spin relaxation is less than a few percent, even after multiple excitation/relaxation cycles. The observed high level of spin preservation may be useful for readout cycling or in quantum information schemes where coupling of neighbor qubits is via orbital excitation.

Coherent superpositions of three states for phosphorous donors in silicon prepared using THz radiation.

Superposition of orbital eigenstates is crucial to quantum technology utilizing atoms, such as atomic clocks and quantum computers, and control over the interaction between atoms and their neighbours is an essential ingredient for both gating and readout. The simplest coherent wavefunction control uses a two-eigenstate admixture, but more control over the spatial distribution of the wavefunction can be obtained by increasing the number of states in the wavepacket. Here we demonstrate THz laser pulse control of Si:P orbitals using multiple orbital state admixtures, observing beat patterns produced by Zeeman splitting. The beats are an observable signature of the ability to control the path of the electron, which implies we can now control the strength and duration of the interaction of the atom with different neighbours. This could simplify surface code networks which require spatially controlled interaction between atoms, and we propose an architecture that might take advantage of this.

Formation of the antiplanar-antiplanar phosphate conformation of dilauroylphosphatidylcholine bilayers.

Infrared spectroscopy was used to investigate lipid conformational changes that occur in dilauroylphosphatidylcholine (diC12PC) bilayers with and without fatty-acid-amino-acids as guest molecules in the membrane. Incorporating 2.5 mole% N-decanoylglycine (decgly) into diC12PC liposomes caused formation of the antiplanar-antiplanar (ap-ap) phosphodiester conformation which was stable in room temperature IR spectra. Several other fatty-acid-amino-acids incorporated into diC12PC bilayers were found to also elicit the ap-ap phosphodiester conformation. Unlike these diC12PC/fatty-acid-amino-acid mixed bilayers, pure diC12PC bilayers would form the ap-ap phosphodiester conformation only under low temperature incubation conditions. Dry diC12PC films incubated at 5 degrees C for 0.5 h (brief incubation) or 16 h (prolonged incubation), and then rapidly hydrated (i.e., vortexed at 25 degrees C in D2O), caused the ap-ap phosphodiester conformation to persist in the diC12PC liposomes equilibrated to room temperature. Slow hydration for 16 h at 5 degrees C in both buffered and non-buffered D2O of diC12PC lipid films also produced the ap-ap phosphodiester conformation. In contrast, slow hydration for 16 h at 5 degrees C in PBS/D2O of diC12PC/decgly mixed films caused the greatest number of ap-ap phosphodiester conformers. Using pure diC12PC bilayers, infrared data indicate that incubation of diC12PC films causes the headgroup phosphodiester conformation to change from gauche-gauche (g-g) conformation to the ap-ap conformation. Under all liposome formation conditions examined, no changes in hydration of either the phosphate group or the carbonyl ester group were detected and in addition, no trans/gauche conformational changes in the acyl chain were observed.

Magnetically induced orientation of phosphatidylcholine membranes.

Lipid bilayers prepared from natural phospholipids orient in magnetic fields with the long axis of the lipid molecules perpendicular to the magnetic field. This magnetically induced orientation was studied at high (11.7 Tesla (T)), mid (9.36 T), and low (4.68 T) magnetic field strengths using lipid aggregates prepared from natural and synthetic phosphatidylcholine analogs. Phosphatidylcholine analogs containing saturated diacylated chains (12 to 16 carbons/chain) exhibited extensive orientation of the lipid when bilayer formation occurred by gentle hydration conditions. Gentle hydration involved incubating dried phosphatidylcholine C above the main phase transition (Tm); brief shaking or swirling by hand was occasionally needed to completely disperse the lipids. The method of bilayer formation significantly influenced the amount of lipid that orients in magnetic fields. Thus the supramolecular structures (and % orientation) above Tm in an 11.7 T field of dimyristoylphosphatidylcholine (DMPC) bilayers are SUV (0%), LUV (approximately 15%), SPLV (approximately 40%), vortexed-MLV (approximately 60%) and non-vortexed MLV (approximately 90%). Single layered vesicles prepared by the REV method exhibited orientation at 11.7 T similar to LUV prepared by freeze thaw cycles. Aqueous dispersions of eggPC prepared by gentle hydration exhibit approximately 40% orientation at 11.7 T which decreased to approximately 30% orientation if 30% cholesterol is added to the membrane. Magnetic orientation of bilayers thus appears to be a general phenomenon for both saturated and unsaturated natural phospholipids either with or without cholesterol in the membrane.

Cholesterol-transfer protein located in the intestinal brush-border membrane. Partial purification and characterization.

Cholesterol absorption by small intestinal brush border membrane vesicles from taurocholate mixed micelles is a second-order reaction. From a comparison of reaction rates and order before and after proteinase K treatment of brush-border membrane vesicles, it is concluded that cholesterol absorption is protein-mediated. It is shown that the desorption of cholesterol from taurocholate mixed micelles is by a factor of about 10(4) faster than that from egg phosphatidylcholine bilayers. When brush border membrane vesicles are stored at room temperature, intrinsic proteinases are activated and proteins are liberated from the brush border membrane. These proteins collected in the supernatant catalyze cholesterol and phosphatidylcholine exchange between two populations of small unilamellar phospholipid vesicles. One of the active proteins present in the supernatant is purified by a two-step procedure involving gel filtration on Sephadex G-75 SF and affinity chromatography on a Nucleosil-phosphatidylcholine column. The protein thus obtained is pure by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. It has an apparent molecular weight of slightly less than 14,000 as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and a value of 11,500 determined by gel filtration on Sephadex G-75 SF.

Papilledema in two patients with acromegaly and intrasellar pituitary tumors.

Two patients had bilateral papilledema complicating acromegaly. Both patients had enlarged blind spots, but otherwise visual fields were normal. Suprasellar extension of the pituitary tumors was diligently sought with the use of visual field examination, pneumoencephalography, internal carotid arteriography, and computed axial tomography, and tumor extension did not exist. Transphenoidal and transethmoidal routes were used to perform partial hypophysectomies in these patients. The procedure was completely successful in one patient and partially successful in the other patient. After hypophysectomy, papilledema resolved in both patients. This beneficial effect may be the result of anatomical changes, the reduction in growth hormone levels, or both. These observations suggest that the acromegaly may be different from papilledema that occurs secondary to suprasellar expansion of pituitary tumors.

Coherent creation and destruction of orbital wavepackets in Si:P with electrical and optical read-out.

The ability to control dynamics of quantum states by optical interference, and subsequent electrical read-out, is crucial for solid state quantum technologies. Ramsey interference has been successfully observed for spins in silicon and nitrogen vacancy centres in diamond, and for orbital motion in InAs quantum dots. Here we demonstrate terahertz optical excitation, manipulation and destruction via Ramsey interference of orbital wavepackets in Si:P with electrical read-out. We show milliradian control over the wavefunction phase for the two-level system formed by the 1s and 2p states. The results have been verified by all-optical echo detection methods, sensitive only to coherent excitations in the sample. The experiments open a route to exploitation of donors in silicon for atom trap physics, with concomitant potential for quantum computing schemes, which rely on orbital superpositions to, for example, gate the magnetic exchange interactions between impurities.

A novel adrenocorticotropin-inducible cytochrome P450 from rat adrenal microsomes catalyzes polycyclic aromatic hydrocarbon metabolism.

7,12-Dimethylbenz(a)anthracene (DMBA) causes massive ACTH-dependent necrosis of the rat adrenal cortex. This may be related to an ACTH-inducible adrenal microsomal cytochrome P450 that metabolizes polycyclic aromatic hydrocarbons (PAH). The proportions of major monooxygenated products of rat adrenal microsomal DMBA metabolism (DMBA-8,9-diol, DMBA-3,4-diol, and DMBA-phenols) differ significantly from that of P450IA1, the most active PAH-metabolizing P450 in rat liver microsomes. After hypophysectomy, both DMBA metabolic activity and a 57K protein which is distinct from P450XXI disappear from rat adrenal microsomes. ACTH restores both 57K protein and DMBA metabolic activity in hypophysectomized rats almost to the levels in intact untreated rats, but not to levels in ACTH-induced intact rats. The 57K protein has been partially purified from solubilized microsomes in a single step, using detergent elution from a new HPLC matrix consisting of monolayers of phosphatidylcholine covalently bound to a silica support. The resulting P450 preparation contains a single major (57K) band, constituting approximately 70% of the total protein (specific content, 2 nmol P450/mg protein; turnover number, 1.5 nmol DMBA min-1. A rabbit polyclonal antibody raised against this preparation also recognizes a single ACTH-inducible 57K rat adrenal microsomal protein on immunoblots and dose-dependently inhibits DMBA metabolism in solubilized reconstituted rat adrenal microsomes. This 57K P450 is immunochemically distinct from rat P450s of the I, II, III, XVII, and XXI families, but it is immunochemically closely related to a 55K benz(a)anthracene-inducible P450 in the 10T1/2 mouse embryo fibroblast cell line.

IAM chromatography: an in vitro screen for predicting drug membrane permeability.

Fluid cell membranes are the main barrier to drug absorption when diffusion limits uptake. Immobilized artificial membranes (IAMs) are solid phase models of fluid membranes that predicted oral drug absorption in mice for a homologous set of cephalosporins. IAMs also predicted drug permeability through Caco-2 cells. Since drug permeability in Caco-2 cells is known to correlate with the oral absorption of drugs in humans, IAMs may also model drug absorption in humans. IAM analysis is experimentally simple, and large-volume screening of experimental compounds for drug absorption is possible.

Localization of inactive cerebrospinal fluid fistulas.

Because of the importance of preoperative localization of dural fistulas, many imaging modalities have been critically evaluated for their role in pinpointing the site of cerebrospinal fluid (CSF) leakage. Twenty-one consecutive patients who were suspected of having a CSF fistula were studied to evaluate magnetic resonance (MR) imaging in locating the fistula. These patients were also studied independently by fine-slice computerized tomography (CT). The MR images demonstrated lesions compatible with dural fistulas in 19 patients, whereas CT demonstrated only seven of these lesions. All of these patients underwent surgical dural repair. The remaining two patients underwent surgical exploration on the basis of the CT findings but no dural fistula was found in either patient. All patients made a good postoperative recovery. One patient developed a postoperative wound infection and in another CSF leakage recurred. Although MR imaging was very precise in locating the CSF fistulas, CT missed a significant number of these lesions and was falsely positive in 9.5% of cases. Therefore, it is concluded that MR imaging is an essential investigation in patients with a suspected dural fistula and should be performed before embarking upon surgery and before assuming natural healing of the CSF fistula.

Affinity purification of phospholipase A2 on immobilized artificial membranes containing and lacking the glycerol backbone.

Immobilized artificial membranes (IAMs) are chromatography surfaces containing monolayers of phospholipid ligands. etherIAM.PCC10/C3 contains the glycerol backbone whereas delta GIAM.PCC10/C3 lacks the glycerol backbone. Affinity purification of PLA2 on these IAM surfaces demonstrated that the surface structural differences were not important for phospholipase A2 (PLA2) binding. This suggests that the chromatographically important binding event involves the PLA2 surface and the monolayer of polar choline headgroups on the IAM surface. After sample loading, short-chain alkylsulfonates were used as low eluotropic strength detergents to remove contaminating proteins, and PLA2 were eluted with CH3CN (30%). Octyllysophosphatidylcholine (0.5%) can replace CH3CN to elute PLA2 from IAM surfaces. The PLA2 purity after IAM chromatography depends on the protein loading; analytical-scale loadings (0.8 mg protein/g IAM) resulted in a PLA2 purity of ca. 70% based on densitometric scans of proteins in polyacrylamide gels after electrophoresis. Preparative loadings of 3.21 mg protein/g IAM resulted in 48% PLA2 purity. Purification of PLA2 to electrophoretic homogeneity was achieved using an IAM column followed by a strong anion-exchange column. These results suggests that IAMs may be used to develop purification methods for PLA2 enzymes obtained from diverse biological specimens.

Immobilized-artificial-membrane chromatography: measurements of membrane partition coefficient and predicting drug membrane permeability.

Immobilized artificial membranes (IAMs) are chromatographic surfaces prepared by covalently immobilizing cell membrane phospholipids to solid surfaces at monolayer densities. IAM surfaces mimic fluid cell membranes. For 23 structurally unrelated compounds, solute capacity factors [log (k'IAM)] measured on IAM columns correlate very well with the solute equilibrium partition coefficients [log (Km)] measured in fluid liposome systems (r = 0.907). This indicates that solute partitioning between the IAM bonded phase and the aqueous mobile phase is similar to the solute partitioning between liposomes and the aqueous phase. IAMs also predicted oral drug absorption in mice and drug permeability through Caco-2 cells. IAM chromatography is experimentally simple and large volume screening of experimental compounds for drug absorption is possible. Solute retention on IAMs was found to be dominated by a partitioning mechanism. The structural requirements for HPLC bonded phases to predict solute-membrane partitioning are briefly discussed.

Mobile phase effects on membrane protein elution during immobilized artificial membrane chromatography.

The eluotropic strength of different mobile phases for eluting membrane proteins from immobilized artificial membrane (IAM) chromatography surfaces was studied. Two protein mixtures containing bovine pancreatic PLA2 were used in this study. Protein mixture I was PLA2 obtained from Sigma which contained approximately 5-10 major protein bands in electrophoretic gels. Protein mixture II was obtained from flesh bovine pancreatic tissue and contained > 100 proteins including the target protein, PLA2. After adsorbing Sigma PLA2 to IAM columns, the elution conditions common to conventional chromatographic methods were evaluated for their ability to selectively purify PLA2. Elution conditions tested were (i) detergent gradients, (ii) salt gradients used during ion-exchange chromatography, (iii) salt conditions used during hydrophobic interaction chromatography, (iv) acetonitrile gradients used during reversed-phase chromatography, and (v) a two-step gradient consisting of first a detergent gradient followed by an acetonitrile gradient. Based on silver-stained electrophoretic protein gels. PLA2 from protein mixture I was purified to electrophoretic homogeneity with 417-fold increase in specific activity in one step using elution condition (v), and PLA2 from protein mixture II was purified in one step (660-fold increase in specific activity) using elution condition (iv). Total protein recovery from IAM columns is 70-100%.

Rapid purification of cotton seed membrane-bound N-acylphosphatidylethanolamine synthase by immobilized artificial membrane chromatography.

N-Acylphosphatidylethanolamine synthase (NAPES) is a membrane-bound enzyme present in cotton seedlings at a concentration of < or = 0.02% of the total protein. NAPES was purified to electrophoretic homogeneity in a single chromatographic step using immobilized artificial membrane (IAM) chromatography. The IAM column used for NAPES purification was etherIAM.PEC10/C3 and this surface contains a monolayer of immobilized phosphatidyl-ethanolamine (PE). Since PE is an analogue of the natural substrate for NAPES, etherIAM.PEC10/C3 columns function as an affinity column for this enzyme. Detergent-solubilized microsomal proteins from cotton were loaded on to the etherIAM.PEC10/C3 column and eluted with buffered mobile phases containing 0.2 mM dimyristoylphosphatidylethanolamine (DMPE) and 2 mM dodecylmaltoside. Little NAPES functional activity eluted if DMPE was removed from the mobile phase. Mobile phase DMPE is also a substrate for NAPES, both the mobile phase and IAM surface contains NAPES substrates. Mobile phase DMPE may function as both a surfactant-type affinity displacing ligand effecting protein elution and also a stabilizing factor of NAPES functional activity. The loading capacity on semi-preparative etherIAM.PEC10/C3 (6.5 x 1.0 cm) columns was ca. 5 mg of total detergent solubilized microsomal proteins, and protein recovery was quantitative. This one-step IAM purification of NAPES resulted in a single band on silver-stained polyacrylamide gels, and 3940 fold increase in NAPES specific activity. The molecular mass of the purified NAPES protein is 64,000. 125I labeled [12-(4-azidosalicyl)amino]dodecanoic acid is a photoreactive fatty acid substrate of NAPES that was used to confirm protein purity.

Calculating number and surface area of liposomes in any suspension.

Simple formulas for calculating the total surface area and number of liposomes in any liposome population are presented. The necessary parameters for calculating these values are the encapsulation ratio (or efficiency) of the population. When tested on theoretical liposome populations, excellent results are obtained regardless of the heterogeneity of the population.