2,218 research outputs found
Coherence of Spin Qubits in Silicon
Given the effectiveness of semiconductor devices for classical computation
one is naturally led to consider semiconductor systems for solid state quantum
information processing. Semiconductors are particularly suitable where local
control of electric fields and charge transport are required. Conventional
semiconductor electronics is built upon these capabilities and has demonstrated
scaling to large complicated arrays of interconnected devices. However, the
requirements for a quantum computer are very different from those for classical
computation, and it is not immediately obvious how best to build one in a
semiconductor. One possible approach is to use spins as qubits: of nuclei, of
electrons, or both in combination. Long qubit coherence times are a
prerequisite for quantum computing, and in this paper we will discuss
measurements of spin coherence in silicon. The results are encouraging - both
electrons bound to donors and the donor nuclei exhibit low decoherence under
the right circumstances. Doped silicon thus appears to pass the first test on
the road to a quantum computer.Comment: Submitted to J Cond Matter on Nov 15th, 200
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio
Mössbauer Spectrometry
Mössbauer spectrometry gives electronic, magnetic, and structural information from within
materials. A Mössbauer spectrum is an intensity of γ-ray absorption versus energy for a
specific resonant nucleus such as ^(57)Fe or ^(119)Sn. For one nucleus to emit a Îł-ray and a second
nucleus to absorb it with efficiency, both nuclei must be embedded in solids, a phenomenon
known as the âMössbauer effect.â Mössbauer spectrometry looks at materials from the
âinside out,â where âinsideâ refers to the resonant nucleus.
Mössbauer spectra give quantitative information on âhyperfine interactions,â which are small
energies from the interaction between the nucleus and its neighboring electrons. The three
hyperfine interactions originate from the electron density at the nucleus (the isomer shift),
the gradient of the electric field (the nuclear quadrupole splitting), and the unpaired electron
density at the nucleus (the hyperfine magnetic field). Over the years, methods have been
refined for using these three hyperfine interactions to determine valence and spin at the
resonant atom. Even when the hyperfine interactions are not easily interpreted, they can
often be used reliably as âfingerprintsâ to identify the different local chemical environments
of the resonant atom, usually with a good estimate of their fractional abundances. Mössbauer
spectrometry is useful for quantitative phase analyses or determinations of the concentrations
of resonant element in different phases, even when the phases are nanostructured or
amorphous.
Most Mössbauer spectra are acquired with simple laboratory equipment and a radioisotope
source, but the recent development of synchrotron instrumentation now allow for measurements
on small 10 ”m samples, which may be exposed to extreme environments of pressure
and temperature. Other capabilities include measurements of the vibrational spectra of the
resonant atoms, and coherent scattering and diffraction of nuclear radiation.
This article is not a review of the field, but an instructional reference that explains principles
and practices, and gives the working materials scientist a basis for evaluating whether or not
Mössbauer spectrometry may be useful for a research problem. A few representative
materials studies are presented
Control and single-shot readout of an ion embedded in a nanophotonic cavity
Distributing entanglement over long distances using optical networks is an intriguing macroscopic quantum phenomenon with applications in quantum systems for advanced computing and secure communication. Building quantum networks requires scalable quantum lightâmatter interfaces based on atoms, ions or other optically addressable qubits. Solid-state emitters5, such as quantum dots and defects in diamond or silicon carbide , have emerged as promising candidates for such interfaces. So far, it has not been possible to scale up these systems, motivating the development of alternative platforms. A central challenge is identifying emitters that exhibit coherent optical and spin transitions while coupled to photonic cavities that enhance the lightâmatter interaction and channel emission into optical fibres. Rare-earth ions in crystals are known to have highly coherent 4fâ4f optical and spin transitions suited to quantum storage and transduction, but only recently have single rare-earth ions been isolated and coupled to nanocavities. The crucial next steps towards using single rare-earth ions for quantum networks are realizing long spin coherence and single-shot readout in photonic resonators. Here we demonstrate spin initialization, coherent optical and spin manipulation, and high-fidelity single-shot optical readout of the hyperfine spin state of single Âčâ·ÂčYbÂłâș ions coupled to a nanophotonic cavity fabricated in an yttrium orthovanadate host crystal. These ions have optical and spin transitions that are first-order insensitive to magnetic field fluctuations, enabling optical linewidths of less than one megahertz and spin coherence times exceeding thirty milliseconds for cavity-coupled ions, even at temperatures greater than one kelvin. The cavity-enhanced optical emission rate facilitates efficient spin initialization and single-shot readout with conditional fidelity greater than 95 per cent. These results showcase a solid-state platform based on single coherent rare-earth ions for the future quantum internet
Coherent multidimensional spectroscopy in the gas phase
Recent work applying multidimentional coherent electronic spectroscopy at
dilute samples in the gas phase is reviewed. The development of refined
phase-cycling approaches with improved sensitivity has opened-up new
opportunities to probe even dilute gas-phase samples. In this context, first
results of 2-dimensional spectroscopy performed at doped helium droplets reveal
the femtosecond dynamics upon electronic excitation of cold, weakly-bound
molecules, and even the induced dynamics from the interaction with the helium
environment. Such experiments, offering well-defined conditions at low
temperatures, are potentially enabling the isolation of fundamental processes
in the excitation and charge transfer dynamics of molecular structures which so
far have been masked in complex bulk environments.Comment: Invited Review Articl
Testing the limits of quantum mechanical superpositions
Quantum physics has intrigued scientists and philosophers alike, because it
challenges our notions of reality and locality--concepts that we have grown to
rely on in our macroscopic world. It is an intriguing open question whether the
linearity of quantum mechanics extends into the macroscopic domain. Scientific
progress over the last decades inspires hope that this debate may be decided by
table-top experiments.Comment: 16 pages, 4 Figures; published version differs by minor editorial
change
Global analysis of coherence and population dynamics in 2D electronic spectroscopy
2D electronic spectroscopy is a widely exploited tool to study excited state dynamics. A high density of information is enclosed in 2D spectra. A crucial challenge is to objectively disentangle all the features of the third order optical signal. We propose a global analysis method based on the variable projection algorithm, which is able to reproduce simultaneously coherence and population dynamics of rephasing and non-rephasing contributions. Test measures at room temperature on a standard dye are used to validate the procedure and to discuss the advantages of the proposed methodology with respect to the currently employed analysis procedures
- âŠ