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IQC Student Seminar featuring Emma Bergeron
Development of InSb Surface Quantum Wells for hybrid superconducting device applications.
Abstract: Surface quantum well (QW) heterostructures in III-V semiconductors are compatible with proximitized superconductivity and offer a scalable planar platform for superconductor-semiconductor systems, such as those suggested for topological quantum computation and those suitable for topological phase transitions involving Majorana zero modes. Amongst III-V binary semiconductors, Indium Antimonide (InSb) has the smallest electron effective mass, highest spin orbit coupling and largest Land´e g-factor. Such material properties makes the pursuit of InSb QWs desirable for a number of quantum device applications, including quantum sensing, quantum metrology, and quantum computing.
Unfortunately, high quality two-dimensional electron gases (2DEGs) in InSb QWs have so far been difficult to realize. InSb QWs have generally relied on the use of modulation doping for 2DEG formation, but these structures have frequently reported issues with parasitic parallel conduction and unstable carrier densities. We report on the transport characteristics of field effect 2DEGs in surface InSb quantum wells which overcome these challenges and are suitable for future hybrid superconducting device applications.
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Quantum Matters Seminar Series: No, you have not discovered a Majorana Fermion
No, you have not discovered a Majorana Fermion
Abstract: Is what I tell myself. There was a time when I thought I may have discovered it, others did too. Around 2012 several groups including ours found evidence of these quantum excitations in electrical circuits containing nanowires of semiconductor covered by a superconductor. The dramatic signatures were peaks in conductance that appeared under conditions expected from theory for Majorana modes, which are their own anti-modes and may possess non-Abelian properties. But a few years later, similar features in the data were identified due to an interesting, but a more mundane effect - which we call trivial states such as Andreev bound states. Over time more and more data pointed at the trivial and not at the exotic explanation. But because Majorana claims kept coming, this led to some digging and even retractions. What we learned after 10 years is that we have a much better handle on what effects show up in these nanowires, which positions us well for the ultimate Majorana discovery which we should be able to tell apart from all the non-Majorana things we saw. The second lesson we learned is that materials quality of device constituents, superconductors and semiconductors, as well as how samples are fabricated - are the make-or-break factors for making this happen. So while I cannot report an exciting physics discovery, I can walk you through the scientific process that took place, a 10-year event of independent value which taught me how to do science better.
Quantum Today: Quantum Energy Teleportation – Activating Ground State Energy
Join us for Quantum Today, where we sit down with researchers from the University of Waterloo’s Institute for Quantum Computing (IQC) to talk about their work, its impact and where their research may lead.
IQC Student Seminar featuring Brendan Bramman
13-level Qudit Measurement Demonstrated in Trapped Ions
IQC Student Seminar featuring Sarah Meng Li
Graphical CSS Code Transformation Using ZX Calculus
Then we focus on two code transformation techniques: code morphing, a procedure that transforms a code while retaining its fault-tolerant gates, and gauge fixing, where complimentary codes (such as the Steane and quantum Reed-Muller codes) can be obtained from a common subsystem code. We provide explicit graphical derivations for these techniques and show how ZX and graphical encoder maps relate several equivalent perspectives on these code transforming operations.
IQC Student Seminar featuring Sainath Motlakunta
Preserving a Qubit During Adjacent Measurements at a Few Micrometers Distance
Abstract:
Protecting a quantum object against irreversible accidental measurements from its surroundings is necessary for controlled quantum operations. This becomes especially challenging or unfeasible if one must simultaneously measure or reset a nearby object's quantum state, such as in quantum error correction.
In atomic systems - among the most established quantum information processing platforms - current attempts to preserve qubits against resonant laser-driven adjacent measurements, waste valuable experimental resources such as coherence time or extra qubits and introduce additional errors. We preserve the quantum state of an 'asset' ion qubit with high fidelity, while a neighbouring qubit at a few microns distance is reset/measured. We achieve < 1 x 10-3 probability of accidental measurement of the asset qubit during a neighbouring qubit reset and < 4 x 10-3 while applying a detection beam on the same neighbour, for 11 μs, at a distance of 6 μm or 4 times the addressing Gaussian beam waist (permitted by the numerical aperture).
These low probabilities correspond to the preservation of the quantum state of the qubit with fidelities above 99.90% (state-reset) and 99.6% (state-measurement). Our results are enabled by precise wavefront control of the addressing optical beams, while utilizing a single ion as a quantum sensor of optical aberrations.
Our work demonstrates the feasibility of in-situ state-reset and measurement operations, building towards enhancements in the speed and capabilities of quantum processors such as in simulating measurement-driven quantum phases and realizing quantum error correction.
IQC Student Seminar featuring Jack Davis
Exploring Wigner Negativity of Pure Spin States on a Spherical Phase Space
The past two decades have largely vindicated the long-held belief that Wigner negativity is an indicator of genuine nonclassicality in quantum systems. Here we will discuss how Wigner negativity manifests in pure spin-j systems using the spherical Wigner function. Common symmetric multi-qubit states are studied and compared, including Bell, W and GHZ states. Spin coherent states are shown to never have vanishing Wigner negativity, in contrast to other phase spaces. Pure states that maximize negativity are determined and analyzed using the Majorana stellar representation. Time permitting, these results will be contrasted with similar works on symmetric state entanglement and other forms of phase-space nonclassicality.
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IQC Student Seminar featuring Matteo Pennacchietti
Near-Unity Entanglement from an Indium-Rich Nanowire Quantum Dot Source Compatible with Efficient Quantum Key Distribution
Thus far, the workhorse platform for generating entangled photons for many quantum information experiments has been spontaneous parametric down conversion (SPDC). However, due to their Poissonian photon statistics, these sources cannot operate in the high efficiency limit without a significant reduction in the degree of entanglement. In contrast, there are no such limits placed on semiconductor quantum dots (QDs) embedded in photonic nanostructures. To date, near-unity entanglement fidelity has not yet been measured from indium-rich QDs, which are promising candidates for realizing such a source. We performed quantum state tomography using single-photon detectors with ultra-low timing jitter and employed two-photon resonant excitation. We measured a raw peak concurrence and fidelity of 95.3 +/- 0.5% and 97.5 +/- 0.8%, respectively, as well as lifetime-weighted average concurrence and fidelity of 0.90 +/- 0.04% and 0.94 +/- 0.04%, respectively. These results conclusively demonstrate that most of the degradation from unity-measured entanglement fidelity in earlier studies was not due to spin dephasing. Additionally, we show that the exciton fine structure splitting, contrary to common understanding, is not in principle a fundamental barrier to implementing QKD with semiconductor QD entangled photon sources.
IQC Student Seminar featuring Omar Hussein
The Cooling and Manipulation of Ultra-Cold Atoms
Ultra-cold atoms have been used to simulate phenomena in condensed matter physics as well as in cosmology such as black holes. In this talk, we will give an overview of the field of ultra-cold atoms by discussing the physics behind the cooling and the manipulation of these atoms. Aimed to show the beautiful physics behind this process, this talk will be easy and general, requiring just an undergraduate level of physics understanding.
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