Topology of the three-qubit space of entanglement types

The three-qubit space of entanglement types is the orbit space of the local unitary action on the space of three-qubit pure states, and hence describes the types of entanglement that a system of three qubits can achieve. We show that this orbit space is homeomorphic to a certain subspace of R^6, which we describe completely. We give a topologically based classification of three-qubit entanglement types, and we argue that the nontrivial topology of the three-qubit space of entanglement types forbids the existence of standard states with the convenient properties of two-qubit standard states.Comment: 9 pages, 3 figures, v2 adds a referenc

Acoustic Analog to Quantum Mechanical Level Splitting

A simple physical system is discussed that mirrors the quantum mechanical infinite square well with a central delta well potential. The physical realization consists of a continuous sound wave traveling in a pair of tubes separated by an adjustable diaphragm. The equivalence between the quantum system and the acoustic system is explored. The analytic solution to the quantum system exhibits level splitting as does the acoustic system

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Pulse propagation of sound, light, and electrons

While electrons have been used for spatial studies since the 1930’s, temporal measurements with electrons are a newer innovation. Using ultrafast electron diffraction, Ahmed Zewail won the Nobel Prize in 1999 for his development of molecular movies. This spurred a movement to improve the temporal resolution by producing smaller-width electron pulses. This thesis describes an electron source that is capable of producing femtosecond electron pulses and its use in testing fundamental physics. Theoretical studies are used to guide the progress of this source in probing fundamental physics. As these electron pulses reach closer to the diffraction limit, quantum mechanical descriptions of these pulses could become more sensible than classical descriptions. A firm background in wave propagation can provide the necessary outlook to distinguish these wave-like properties. In this thesis, an acoustic apparatus is developed that can provide such a background. Physical demonstrations of quantum effects, such as level splitting, avoided crossing, and the formation of band gaps, are done with this acoustic system. This system also lends itself to optical analogies which are presented. These analogies could be used to predict the dynamics of the electron pulses from our source. Temporal limits of the electron source are explored at various operating parameters, which provide information on the emission process. These findings show that the source can be coupled with a drift tube to make a time-of-flight energy analyzer that could rival state-of-the-art devices. The possibility of fundamental studies, such as testing the time dependence of the Pauli exclusion principle, is explored with this source. A theoretical model is used to determine the viability of coupling this source with dispersion compensation techniques to produce pulse widths in the attosecond domain. The wide spread of uses shows that the source is not only useful but versatile

Experimental Observation of Time-Delays Associated with Electric Matteucci–Pozzi Phase Shifts

In 1985, Matteucci and Pozzi (1985 Phys. Rev. Lett. 54 2469) demonstrated the presence of a quantum mechanical phase shift for electrons passing a pair of oppositely charged biprism wires. For this experimental arrangement no forces deflect the electrons. Consequently, the result was reported as a non-local type-2 Aharonov–Bohm effect. Boyer (2002 Found. Phys. 32 41–50; 1987 Nuovo Cimento B 100 685–701) showed theoretically that the Matteucci–Pozzi effect could be associated with a time delay caused by a classical force. We present experimental data that confirm the presence of a time delay. This result is in contrast to the situation for the original magnetic Aharonov–Bohm effect. On similar theoretical grounds, Boyer has also associated classical forces and time delays with the magnetic Aharonov–Bohm effect. Recently, we reported the absence of such observable time delays. The contrast with our current work illustrates the subtle nature of Aharonov–Bohm effects

Exploring temporal and rate limits of laser-induced electron emission

To achieve high temporal resolution for ultrafast electron diffraction, Zewail (Proc. Natl Acad. Sci. USA 102, 7069 (2005)) has proposed to use high repetition rate, ultrafast electron sources. Such electron sources emitting one electron per pulse eliminate Coulomb broadening. High repetition rates are necessary to achieve reasonable data acquisition times. We report laser-induced emission from a nanometre-sized tip at one electron per pulse with a 1 kHz repetition rate in the femtosecond regime. This source, combined with 1 MHz repetition rate lasers that are becoming available, will be a primary candidate for next generation ultrafast, high-coherence electron diffraction experiments. We also report that the measured energy bandwidth of our electron source does not support sub-cycle electron emission. This result addresses a current debate on ultrafast nanotip sources. Regardless of the limited bandwidth, this source may be used in conjunction with a recently proposed active dispersion compensation technique (Proc. Natl Acad. Sci. USA 104, 18409 (2007)) to deliver attosecond electron pulses on a target

A high repetition rate time-of-flight electron energy analyzer

We demonstrate a time-of-flight electron energy analyzer that operates at an 80 MHz repetition rate. The analyzer yields an energy resolution of 40 meV for 3 eV electrons. The energy resolution limit is dominated by the detector time (or temporal) resolution. With a currently available detector with a temporal resolution of 100 ps, we predict an energy resolution of less than 1 meV for 200 meV electrons. This makes high repetition rate time-of-flight energy analyzers a promising low-technology alternative to current state-of-the-art techniques

Development Practices and Ordinances Predict Inter-City Variation in Florida Urban Tree Canopy Coverage

Many cities around the world have set ambitious urban tree canopy cover goals, with the expectation that urban forests will provide ecosystem services as functional green infrastructure. Numerous studies have examined intra-city spatial patterns in urban tree canopy (UTC) and found that UTC relates to socioeconomic indicators and urban form. Additionally, a few studies have shown local regulations can be linked to increased tree cover. However, the relationship between UTC and governance across different cities has not been well-explored. To address this gap, we compared the management practices enacted by 43 municipalities in Florida (United States) to investigate their potential impact on tree canopy coverage. UTC was assessed through visual interpretation of aerial images. We used multiple linear regression to predict inter-city variation in UTC based on 1) municipal forestry management practices, including whether the municipality had an arborist, tree ordinances, a municipal tree inventory, and a canopy cover goal, and 2) community sociodemographic data. UTC ranged between 17.6% and 63.3% among the municipalities assessed, with an average UTC of 33.7%. Two factors significantly predicted canopy coverage. Housing density had a negative relationship with tree canopy (P-value = 0.0116). In contrast, municipalities with heritage tree protections had 6.7% more canopy coverage (P-value = 0.0476). Future research should continue to consider the potential impacts of governance structures on the spatiotemporal dynamics of inter- and intra-city UTC patterns