WIPC 2017 - Day 2

Divergenceless methods to quantify vacuum correlations in quadratically coupled fields

The vacuum state of a quantum field possesses correlations, both classical and quantum, between spacelike separated regions [1,2]. By reading out these correlations, we can gather information about the structure of spacetime [3,4]. Additionally, vacuum correlations can, in principle, be used as a resource for quantum communication and other quantum information tasks. Past works have studied this phenomenon, called entanglement harvesting [5,6], in the case of detectors coupling linearly to a bosonic field; e.g. two atoms coupled to the electromagnetic field.

We present new divergence-free methods to study correlations harvested from quadratically coupled fields to a particle detectors (such as Unruh-DeWitt). These methods become relevant in the study of vacuum entanglement of fermionic fields and interacting bosonic theories. For example, the entanglement structure of the fermionic vacuum has not yet been studied in detail. The chief reason is that we lacked an adequate divergence-free equivalent to the Unruh-DeWitt particle detector model for fermionic fields [7].

We expect that these studies will shed light on the nature of fermionic field vacuum entanglement, which displays distinctive features not present in the bosonic case as observed in the study of the Unruh effect [8,9].

Work in collaboration with: Eduardo Martín-Martínez and Robert B. Mann.

[1] S. J. Summers and R. F. Werner, Phys. Lett. A 110 , 257 (1985).
[2] S. J. Summers and R. F. Werner, J. Math. Phys. 28, 2
[3] G. V. Steeg and N. C. Menicucci, Phys. Rev. D 79, 044027 (2009).
[4] E. Martin-Martinez, A. R. H. Smith, D. R. Terno, Phys. Rev. D 93, 044001 (2016)

Affiliation: Institute for Quantum Computing

Zero Modes and Entanglement Entropy

Ultraviolet divergences are widely discussed in studies of entanglement entropy. Also present, but much less understood, are infrared divergences due to zero modes in the field theory. In this talk, I will discuss the importance of carefully handling zero modes in entanglement entropy. I will give an explicit example for a chain of harmonic oscillators in 1D, where a mass regulator is necessary to avoid an infrared divergence due to a zero mode. I will also comment on a surprising contribution of the zero mode to the UV-scaling of the entanglement entropy.

Affiliation: University of Waterloo and Perimeter Institute

Quantum energy teleportation as a tool to keep quantum computers cool

Combining quantum thermodynamics with concepts of quantum field theory such as the quantum interest conjecture and quantum energy teleportation, we show that a long standing upper bound on the cooling limits of algorithmic cooling methods can be broken by exploiting system correlations due to internal interaction. In particular, we exploit quantum energy teleportation to consume correlations present due to the internal interaction while extracting work locally, resulting in the purification of a target qubit. Controlled purification of quantum states is at the core of practical applications of quantum information science, especially for quantum computation. This preparation is required for initializing quantum information processors, and for a reliable supply of ancilla qubits that satisfy the fault-tolerance threshold for quantum error correction.

Affiliation: Institute for Quantum Computing

Connections between Bell inequalities and symmetric extensions

Symmetric extendibility of quantum states has been proven to be useful in various areas of quantum information and quantum communication such as detection of entanglement, determining entanglement distillability, and characterizing anti-degradable channels. Thus, it is important to determine whether any quantum state can possess a symmetric extension or not. So far, the necessary and sufficient conditions for the existence of symmetric extension of quantum states has been known for only 2-qubit states, the question being open for 2-qudit states. We provide a sufficient condition for the non-existence of 3-qudit symmetric extension of any 2-qudit state using the existence of nonlocal quantum correlations in the quantum state measured via Bell inequalities. First, we prove that any 2-qubit state that violates the CHSH inequality cannot have a symmetric extension. Next, we prove that if a 2-qudit Bell inequality is monogamous, then any 2-qudit state that violates this inequality cannot have a symmetric extension. Finally, we conjecture Bell CGLMP inequality for 2-qutrit states to be monogamous using numerical evidences. A key feature of our work is that our analysis of qudit states is general and provides a sufficient condition for testing the symmetric extension of quantum states of any dimension.

Affiliation: Institute for Quantum Computing

Quantum Tunneling with a Lorentzian Path Integral

We describe the tunneling of a quantum mechanical particle with a Lorentzian (real-time) path integral. The analysis is made concrete by the application to the inverted harmonic oscillator potential, where the path integral is known exactly. We apply Picard-Lefschetz theory to the time integral of the Feynman propagator at fixed energy, and show that the Euclidean integration contour is obtained as a Lefschetz thimble, or a sum of them, in a suitable limit. Picard-Lefschetz theory is used to make the integral manifestly convergent and is also essential for the saddle point or semi-classical approximation. The very simple example of the inverted harmonic oscillator presents many of the interesting feature found when dealing with instantons, such as the Stokes phenomenon and multiple relevant complex saddles.

Affiliation: Perimeter Institute

Single molecule visualization of topology-mediated interactions in supercoiled DNA

DNA topology is closely linked to important cellular processes such as transcription, DNA replication, and DNA repair. In the nucleus, DNA structure has long been known to consist of two strands of nucleotides wrapped around each other into a double helix. Higher order structures that are potentially important for cellular function are also known to occur in DNA, and are driven by what is called supercoiling. This term refers to the double helix winding further around itself, creating torsional strain in the DNA that can be relieved via higher order structures or local unwinding of the double helix at specific sites. These tend to correspond to important physiological regions that control for DNA replication and gene expression. While the static state of these structural changes is well understood, very little is known about supercoil-induced unwinding dynamics.

We developed a method that monitors the unwinding of a specific site of bacterial DNA into two single strands by probing the site with a fluorescent strand of DNA designed to bind specifically to the unwound site. Our technique allows us to visualize DNA interactions and kinetics without chemically or mechanically interfering with the DNA’s structure, while obtaining high statistics under different experimental conditions. We used this to quantitatively investigate the effects of temperature and supercoiling on bacterial DNA unwinding, taking an important step toward understanding cellular processes.

Affiliation: University of Toronto and McGill University

The effect of solar rotation on stratospheric ozone as observed by OSIRIS

The amount of solar radiation reaching the Earth’s atmosphere varies with both the 11 year solar cycle and the 27 day solar rotation period. Ozone in the middle atmosphere is largely created through photolysis at ultraviolet wavelengths. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) has been in orbit on the Odin satellite since late 2001. OSIRIS ozone profiles were used to investigate the effect of changes in solar ultraviolet flux on stratospheric ozone concentrations. Analysis was done using the fast Fourier transform, continuous wavelet transform, and cross correlations between the ozone time series and a solar proxy.

The effects of changes in temperature were also considered. Results were consistent with those from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) from 2003 to 2008 and the Microwave Limb Sounder (MLS) from 2004 to 2007. For the time period from 2002 to 2015 a 0.1% change in ozone concentration occurred for a 1% change in solar ultraviolet flux. The validity of using OSIRIS data to analyze the effect of solar rotation on stratospheric ozone has been confirmed. This provides a larger data set and insight on the current relatively weak solar cycle that can be used in future climate modeling.

Affiliation: University of Saskatchewan

The still unexplained increase of atmospheric methane and heavy methane

Methane (CH4) is the second most important greenhouse gas emitted by human activities in the Earth’s atmosphere. Although it is roughly 200 times less abundant than carbon dioxide, it is a 28 times more potent greenhouse gas. Approximately one fifth of the changes in the Earth’s balance energy caused by human-linked greenhouse gases since the beginning of industrialization (~1750) is due to methane.

Methane is emitted by both natural sources and human activities. Indeed, methane can be emitted to the atmosphere through coal mining, oil and gas exploitation, rice cultures, domestic ruminant animals, biomass burning, waste management, wetlands, termites, methane hydrates and ocean. In the atmosphere, due to its role on the oxidizing capacity of the atmosphere, methane is also called the detergent of the atmosphere.

Since the beginning of the industrialization, atmospheric methane concentrations have increased by 260% to reach 1824 pbb in 2013. From the 1980s until the beginning of the 1990s, atmospheric methane was significantly on the rise, then stabilized during 1999-2006 to rise again afterwards. To this day, the source or sink responsible of this latter increase remains unexplained.

Through each emission process, heavy molecules of methane (with one additional neutron either on a carbon or on one hydrogen atom) are emitted along methane (12CH4). The main heavy molecules of methane, called isotopologues (13CH4 and CH3D), are respectively ~110 and ~60 000 times less abundant than methane. Despite their small abundances, they give crucial information on the concentration of methane in the atmosphere and its evolution. Indeed, both isotopologues are emitted with specific emission ratio depending on the emission sources. Determining isotopic ratio of atmospheric methane is therefore a unique tracer of its budget.

While the non-monotonous trend of methane is subject of an extensive number of studies, to our knowledge, no study of the isotopic ratio of methane derived from ground-based solar observations has been published to date. Measurements of heavy methane from Fourier Transform InfraRed spectra recorded with state of the art spectrometers installed at Eureka [Arctic, Canada] and Toronto [Ontario, Canada] will help fill this gap.

Affiliation: University of Toronto

Experimental study by visualisation of behavioural properties of vortex structures on the upper surface of an ogive

Methane (CH4) is the second most important greenhouse gas emitted by human activities in the Earth’s atmosphere. Although it is roughly 200 times less abundant than carbon dioxide, it is a 28 times more potent greenhouse gas. Approximately one fifth of the changes in the Earth’s balance energy caused by human-linked greenhouse gases since the beginning of industrialization (~1750) is due to methane. Methane is emitted by both natural sources and human activities.

Indeed, methane can be emitted to the atmosphere through coal mining, oil and gas exploitation, rice cultures, domestic ruminant animals, biomass burning, waste management, wetlands, termites, methane hydrates and ocean. In the atmosphere, due to its role on the oxidizing capacity of the atmosphere, methane is also called the detergent of the atmosphere. Since the beginning of the industrialization, atmospheric methane concentrations have increased by 260% to reach 1824 pbb in 2013.

From the 1980s until the beginning of the 1990s, atmospheric methane was significantly on the rise, then stabilized during 1999-2006 to rise again afterwards. To this day, the source or sink responsible of this latter increase remains unexplained.

Through each emission process, heavy molecules of methane (with one additional neutron either on a carbon or on one hydrogen atom) are emitted along methane (12CH4). The main heavy molecules of methane, called isotopologues (13CH4 and CH3D), are respectively ~110 and ~60 000 times less abundant than methane. Despite their small abundances, they give crucial information on the concentration of methane in the atmosphere and its evolution. Indeed, both isotopologues are emitted with specific emission ratio depending on the emission sources. Determining isotopic ratio of atmospheric methane is therefore a unique tracer of its budget.

While the non-monotonous trend of methane is subject of an extensive number of studies, to our knowledge, no study of the isotopic ratio of methane derived from ground-based solar observations has been published to date. Measurements of heavy methane from Fourier Transform InfraRed spectra recorded with state of the art spectrometers installed at Eureka [Arctic, Canada] and Toronto [Ontario, Canada] will help fill this gap.

Affiliation: University of Valenciennes

Surface currents in the Fraser River plume in the Strait of Georgia observed by high frequency radar and GPS-tracked drifters

The Fraser River is the largest undammed river on the west coast of North America, and its discharge into the Strait of Georgia near Vancouver has a substantial impact on the local oceanography.  The river-ocean interface is a complex region, and understanding how these waters flow and mix has a bearing on practical issues such as determining the fate of river-borne contaminants (three wastewater facilities discharge into the Fraser River). 

In an effort to understand the fluid dynamics of this system, and how contaminants disperse in the Strait of Georgia, two different observational data sets are compared critically:  GPS tracks from drifting buoys, and spatially-resolved flow measurements from high frequency radar backscatter.  The results shed light on both the advantages and disadvantages of these approaches, and the oceanic forces at work in the Strait of Georgia.

Affiliation: University of British Columbia