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<p class="MsoNormal" style="border:none;padding:0cm">Dear All,<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Next week’s colloquium will be given by Dr Edward Laird (Materials, Oxford) on “Spin qubits and radio-frequency optomechanics with carbon nanotubes”. As usual, tea/coffee will be served after the colloquium
in the Common Room.<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Title: Spin qubits and radio-frequency optomechanics with carbon nanotubes
<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Speaker: Edward Laird, Department of Materials, University of Oxford<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Time/Date: 3pm Wednesday 28<sup>th</sup> October 2015<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Venue: John Anderson Building JA3.14<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Abstract:<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Carbon nanotubes are versatile materials in which many aspects of condensed matter physics come together. The chemical vapour deposition process through which nanotubes are synthesized leaves very low disorder;
by incorporating these pristine nanotubes we can fabricate clean electrical devices in which delicate effects can be studied. Recently, we developed the technology of stamping, which allows single nanotubes to be positioned in quantum dot devices, and is compatible
with many other fabrication techniques. I will present two sets of experiments that make use of the unique properties of clean nanotube devices.<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">I will begin by describing the first qubit in this material, the spin-valley qubit. This makes use of both the electron spin and the valley magnetic moment, which are coupled by the spin-orbit interaction.
To realize this qubit, we first used gate potentials to define a double quantum dot. Then, we made use of the Pauli exclusion principle to configure the device as an electrical spin filter. Finally, we exploited a bend in the nanotube to manipulate the qubit
electrically, reading it out and characterizing its coherence properties via the current through the device.<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">In the second part of the talk, I will present electromechanical measurements of vibrating nanotubes. Nanotubes combine light mass (leading to large zero-point motion) and high stiffness (leading to large
mode spacing), making them potentially interesting for studying the quantum limit of mechanical motion. We have measured nanotube mechanical modes with frequencies as high as 39 GHz, implying efficient cooling to the ground state in a standard laboratory cryostat.
We have also shown how to measure nanotube mechanics without passing a current, by coupling optomechanically to a radio-frequency tank circuit. I will discuss how we may build on these experiments to study quantum effects in a vibrating nanotube.<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">References<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">“A valley-spin qubit in a carbon nanotube”<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">EA Laird, F Pei, LP Kouwenhoven<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Nature Nanotechnology 8, 565-568 (2013)<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">“A high quality factor carbon nanotube mechanical resonator at 39 GHz”<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">EA Laird, F Pei, W Tang, GA Steele, LP Kouwenhoven<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Nano Letters 12 193-197 (2011)<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">“Quantum transport in carbon nanotubes”<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">E.A. Laird, F. Kuemmeth, G. Steele, K. Grove-Rasmussen, J. Nygård, K. Flensberg, L.P. Kouwenhoven<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm">Reviews of Modern Physics 87, 703 (2015)<o:p></o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
<p class="MsoNormal" style="border:none;padding:0cm"><o:p> </o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Dr Daniel K. L. Oi<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Lecturer, Quantum Information<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Computational Nonlinear & Quantum Optics<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">SUPA Department of Physics<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">University of Strathclyde<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Glasgow G4 0NG<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">United Kingdom<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Tel: +44 141 548 3112<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Fax: +44 141 552 2891<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">Web: cnqo.phys.strath.ac.uk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB">The Department of Physics, University of Strathclyde, Rated No. 1 in the UK by the UK led Research Excellence Framework (REF2014).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-GB"><br>
The University of Strathclyde is a charitable body, registered in Scotland, number SCO15263<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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