An open-source high-frequency lock-in amplifier.

We present characterization of a lock-in amplifier based on a field programmable gate array capable of demodulation at up to 50 MHz. The system exhibits 90 nV/√Hz of input noise at an optimum demodulation frequency of 500 kHz. The passband has a full-width half-maximum of 2.6 kHz for modulation frequencies above 100 kHz. Our code is open source and operates on a commercially available platform.

An analytical model for the detection of levitated nanoparticles in optomechanics.

Interferometric position detection of levitated particles is crucial for the centre-of-mass (CM) motion cooling and manipulation of levitated particles. In combination with balanced detection and feedback cooling, this system has provided picometer scale position sensitivity, zeptonewton force detection, and sub-millikelvin CM temperatures. In this article, we develop an analytical model of this detection system and compare its performance with experimental results allowing us to explain the presence of spurious frequencies in the spectra.

Free Nano-Object Ramsey Interferometry for Large Quantum Superpositions.

We propose an interferometric scheme based on an untrapped nano-object subjected to gravity. The motion of the center of mass (c.m.) of the free object is coupled to its internal spin system magnetically, and a free flight scheme is developed based on coherent spin control. The wave packet of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. A gravity induced dynamical phase (accrued solely on the spin state, and measured through a Ramsey scheme) is used to reveal the above spatially delocalized superposition of the spin-nano-object composite system that arises during our scheme. We find a remarkable immunity to the motional noise in the c.m. (initially in a thermal state with moderate cooling), and also a dynamical decoupling nature of the scheme itself. Together they secure a high visibility of the resulting Ramsey fringes. The mass independence of our scheme makes it viable for a nano-object selected from an ensemble with a high mass variability. Given these advantages, a quantum superposition with a 100 nm spatial separation for a massive object of 10^{9} amu is achievable experimentally, providing a route to test postulated modifications of quantum theory such as continuous spontaneous localization.

Burning and graphitization of optically levitated nanodiamonds in vacuum.

A nitrogen-vacancy (NV(-)) centre in a nanodiamond, levitated in high vacuum, has recently been proposed as a probe for demonstrating mesoscopic centre-of-mass superpositions and for testing quantum gravity. Here, we study the behaviour of optically levitated nanodiamonds containing NV(-) centres at sub-atmospheric pressures and show that while they burn in air, this can be prevented by replacing the air with nitrogen. However, in nitrogen the nanodiamonds graphitize below ≈10 mB. Exploiting the Brownian motion of a levitated nanodiamond, we extract its internal temperature (T(i)) and find that it would be detrimental to the NV(-) centre's spin coherence time. These values of T(i) make it clear that the diamond is not melting, contradicting a recent suggestion. Additionally, using the measured damping rate of a levitated nanoparticle at a given pressure, we propose a new way of determining its size.

Matter-wave interferometry of a levitated thermal nano-oscillator induced and probed by a spin.

We show how the interference between spatially separated states of the center of mass (c.m.) of a mesoscopic harmonic oscillator can be evidenced by coupling it to a spin and performing solely spin manipulations and measurements (Ramsey interferometry). We propose to use an optically levitated diamond bead containing a nitrogen-vacancy center spin. The nanoscale size of the bead makes the motional decoherence due to levitation negligible. The form of the spin-motion coupling ensures that the scheme works for thermal states so that moderate feedback cooling suffices. No separate control or observation of the c.m. state is required and thereby one dispenses with cavities, spatially resolved detection, and low-mass-dispersion ensembles. The controllable relative phase in the Ramsey interferometry stems from a gravitational potential difference so that it uniquely evidences coherence between states which involve the whole nanocrystal being in spatially distinct locations.

Measuring central-spin interaction with a spin-bath by pulsed ENDOR: Towards suppression of spin diffusion decoherence.

We present pulsed electron-nuclear double resonance (ENDOR) experiments which enable us to characterize the coupling between bismuth donor spin-qubits in Si and the surrounding spin-bath of (29)Si impurities which provides the dominant decoherence mechanism (nuclear spin diffusion) at low temperatures (< 16 K). Decoupling from the spin-bath is predicted and cluster correlation expansion simulations show near-complete suppression of spin diffusion, at optimal working points. The suppression takes the form of sharply peaked divergences of the spin diffusion coherence time, in contrast with previously identified broader regions of insensitivity to classical fluctuations. ENDOR data shows anisotropic contributions are comparatively weak, so the form of the divergences is independent of crystal orientation.

Electronic spin storage in an electrically readable nuclear spin memory with a lifetime >100 seconds.

Electron spins are strong candidates with which to implement spintronics because they are both mobile and able to be manipulated. The relatively short lifetimes of electron spins, however, present a problem for the long-term storage of spin information. We demonstrated an ensemble nuclear spin memory in phosphorous-doped silicon, which can be read out electrically and has a lifetime exceeding 100 seconds. The electronic spin information can be mapped onto and stored in the nuclear spin of the phosphorus donors, and the nuclear spins can then be repetitively read out electrically for time periods that exceed the electron spin lifetime. We discuss how this memory can be used in conjunction with other silicon spintronic devices.

Bismuth qubits in silicon: the role of EPR cancellation resonances.

We investigate electron paramagnetic resonance spectra of bismuth-doped silicon, at intermediate magnetic fields B≃0.1-0.6 T, theoretically and experimentally (with 9.7 GHz X-band spectra). We identify a previously unexplored regime of "cancellation resonances," where a component of the hyperfine coupling is resonant with the external field. We show that this regime has experimentally accessible consequences for quantum information applications, such as reduction of decoherence, fast manipulation of the coupled electron-nuclear qubits, and spectral line narrowing.

High-Field Phenomena of Qubits.

Electron and nuclear spins are very promising candidates to serve as quantum bits (qubits) for proposed quantum computers, as the spin degrees of freedom are relatively isolated from their surroundings and can be coherently manipulated, e.g., through pulsed electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). For solid-state spin systems, impurities in crystals based on carbon and silicon in various forms have been suggested as qubits, and very long relaxation rates have been observed in such systems. We have investigated a variety of these systems at high magnetic fields in our multifrequency pulsed EPR/ENDOR (electron nuclear double resonance) spectrometer. A high magnetic field leads to large electron spin polarizations at helium temperatures, giving rise to various phenomena that are of interest with respect to quantum computing. For example, it allows the initialization of both the electron spin as well as hyperfine-coupled nuclear spins in a well-defined state by combining millimeter and radio-frequency radiation. It can increase the T(2) relaxation times by eliminating decoherence due to dipolar interaction and lead to new mechanisms for the coherent electrical readout of electron spins. We will show some examples of these and other effects in Si:P, SiC:N and nitrogen-related centers in diamond.

Fast nuclear spin hyperpolarization of phosphorus in silicon.

We experimentally demonstrate a method for obtaining nuclear spin hyperpolarization, that is, polarization significantly in excess of that expected at thermal equilibrium. By exploiting a nonequilibrium Overhauser process, driven by white light irradiation, we obtain more than 68% negative nuclear polarization of phosphorus donors in silicon. This polarization is reached with a time constant of approximately 150 sec, at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain such large polarizations is discussed with regards to its significance for quantum information processing and magnetic resonance imaging.

Long-lived spin coherence in silicon with an electrical spin trap readout.

Pulsed electrically detected magnetic resonance of phosphorous (31P) in bulk crystalline silicon at very high magnetic fields (B0>8.5 T) and low temperatures (T=2.8 K) is presented. We find that the spin-dependent capture and reemission of highly polarized (>95%) conduction electrons by equally highly polarized 31P donor electrons introduces less decoherence than other mechanisms for spin-to-charge conversion. This allows the electrical detection of spin coherence times in excess of 100 mus, 50 times longer than the previous maximum for electrically detected spin readout experiments.

Nanoscale solid-state quantum computing.

Most experts agree that it is too early to say how quantum computers will eventually be built, and several nanoscale solid-state schemes are being implemented in a range of materials. Nanofabricated quantum dots can be made in designer configurations, with established technology for controlling interactions and for reading out results. Epitaxial quantum dots can be grown in vertical arrays in semiconductors, and ultrafast optical techniques are available for controlling and measuring their excitations. Single-walled carbon nanotubes can be used for molecular self-assembly of endohedral fullerenes, which can embody quantum information in the electron spin. The challenges of individual addressing in such tiny structures could rapidly become intractable with increasing numbers of qubits, but these schemes are amenable to global addressing methods for computation.

Synthetic graft placement in the treatment of fascial dehiscence with necrosis and infection.

OBJECTIVE: The objective of this study was to describe the use of synthetic grafts in repairing fascial dehiscence complicated by fascial necrosis and infection after obstetric and gynecologic operations. STUDY DESIGN: A retrospective review of the operating room records at Hutzel Hospital (Detroit, Mich) was performed to find all cases of fascial dehiscence repaired during a 6-year period between January 1, 1991, and December 31, 1996. Patients with partial or complete disruption of the fascia with evidence of fascial necrosis and infection were included in this study. Demographic information; the initial surgical procedure, including type of incision; suture material; use of synthetic graft and closure technique for repair of dehiscence; postoperative complications, microbiologic results; antibiotic therapy; subsequent operations; length of hospital stay; and late complications were recorded. RESULTS: During the study period 52 patients underwent repair of fascial dehiscence; 36 of these had concurrent fascial necrosis and infection, including 4 women with necrotizing fasciitis. Eighteen patients were from the obstetric service and 18 were from the benign or cancer gynecology service. Ninety-one bacterial isolates were recovered from the infected wounds. Extensive fascial resection precluded closure without tension in 18 cases and necessitated synthetic graft placement to prevent evisceration. Graft materials included polypropylene (11 cases) and polyglactin (7 cases). Late complications of graft placement included extrusion of the graft in 3 patients and incisional hernia in 1. CONCLUSIONS: Extensive fascial débridement with resection prevents primary closure of wound dehiscence. Synthetic grafts permit primary closure of large fascial defects and can be used with extensive débridement in the presence of infection.

Total colpocleisis for vaginal eversion.

OBJECTIVE: This report describes a technique for total colpocleisis performed on women with posthysterectomy vaginal eversion and presents the outcome of this surgery. STUDY DESIGN: Thirty-three women, aged 51 to 94 years (78.1 +/- 8.8, average +/- SD) with vaginal eversion were treated with total colpocleisis. Twenty-four women had previously undergone a total of 40 operations for prolapse, and many had a massive prolapse with scarring and ulceration. Five women had stress incontinence, and an additional 12 had poor urethral support without stress incontinence. In association with colpocleisis, 14 had suburethral plication of the endopelvic fascia; two, needle suspensions; and one, a pubovaginal sling. Three had a perineorrhaphy. RESULTS: Operations lasted from 30 to 205 minutes (101 +/- 33.4, average +/- SD), and the estimated blood loss ranged from 20 to 750 ml (206 +/- 171, average +/- SD). No operative complications occurred. Postoperatively, congestive heart failure developed in two women and one had pneumonia; all illnesses resolved with appropriate therapy. There were no complications at the operative site. Average follow-up was 35 (+/-48) months. All women were initially cured of the vaginal eversion. Recurrent eversion developed in one woman 1 year after surgery and was successfully treated with repeat colpocleisis. Of five women with preoperative stress incontinence, four were cured and one lost to follow-up. No new stress incontinence occurred. CONCLUSION: Total colpocleisis is an effective operation for the treatment of vaginal eversion in selected situations. When defective urethral support is corrected at the time of the operation, postoperative incontinence is not usually a problem.

Treatment of uterine and vaginal prolapse.

As stated earlier, we as gynecologic surgeons are going to see more of these problems as we experience the increased longevity of our patients. With the patients best interest in mind, it is suggested that one inexperienced in the performance of the sacrospinous ligament suspension should serve a tutorial with one who had considerable experience with this procedure. Contrariwise, the colpectomy followed by a total colpocleisis is so straightforward that my teaching is, "See one; do one; teach one!"

Treatment of refractory ovarian carcinoma with paclitaxel and cisplatin after treatment failure with single-agent paclitaxel.

The clinical response to paclitaxel and cisplatin was evaluated in fifteen patients with refractory epithelial ovarian cancer who failed to respond to treatment with single agent paclitaxel. Patients received combination chemotherapy every 3 weeks with both 135 mg/m2 (9) or 175 mg/m2 (6) of paclitaxel and 50 mg/m2 (2), 75 mg/m2 (4) or 100 mg/m2 (9) of cisplatin. There was 1 complete clinical response, with 2 partial clinical responses for an overall response rate of 20%. The progression free interval was 6+ months for the complete responder and 9.5+ months for the partial responders. Overall five (33%) patients experienced an improvement in clinical response over that seen with paclitaxel alone, and 5 patients have died. Improvement in clinical response with combination chemotherapy compared to paclitaxel alone was positively associated with the cisplatin dose; while disease progression and death were inversely associated with the paclitaxel dose. Addition of cisplatin to paclitaxel may be useful in the treatment of patients who fail to respond to paclitaxel alone.

[100 years radical abdominal operation of cervix carcinoma: in memory of Wertheim's predecessors]. / 100 Jahre abdominale Radikaloperation des Zervixkarzinoms: Erinnerung an Wertheims Vorläufer.

1895 was a crucial year in the course of the development of abdominal radical surgery for effective treatment of cervical cancer. In March of 1895, Ries presented the rationale of modern radical hysterectomy and was the first to call for systematic removal of pelvic lymph nodes. Independently, Clark in Baltimore, Rumpf in Berlin, and Latzko in Vienna performed the first radical hysterectomies. This article is dedicated to the memory of the contributions by these four pioneers of surgical gynecology presented in 1895.

The role of vaginal hysterectomy in the treatment of endometrial carcinoma.

Between 1964 and 1991, vaginal hysterectomy was performed in 60 patients with clinical stage I endometrial carcinoma, who were not considered candidates for the conventional surgical approach. Of these patients, 66.7% were obese with a median weight of 235 pounds. Other risk factors included hypertension (63%), diabetes mellitus (34%), cardiac disease (28%) and pulmonary disease (12%). Operative mortality was 0%. The complication rate was 14%, with four patients requiring transfusions and four patients developing vaginal cuff cellulitis. Forty per cent of patients received adjuvant pre- or postoperative radiation therapy. Crude survival at 5 and 10 years was 91.1% and 87.1%, respectively. However, only one patient died from disease 6 years after primary treatment. Although we consider surgical staging as the standard of care for the treatment of endometrial cancer, vaginal hysterectomy has a definite place in the management of patients with good prognostic criteria who are at high operative risk for the standard surgical approach.