Andreas Wallraff (ETH Zurich, Switzerland)

Superconducting circuits are a prime contender for realizing universal quantum computation and solving noisy intermediate-scale quantum (NISQ) problems on fault-tolerant or non-error-corrected quantum processors, respectively. In this talk, I will present elements of an architecture which allows for fast, high-fidelity, single shot qubit read-out [1], for unconditional reset [2], and can be multiplexed [3]. Integrating multiple qubits in a single device, we evaluate performance metrics such as the single and two-qubit gate fidelity and the qubit readout fidelity. We also test the performance of the architecture in parity measurements with real-time feedback, which is a basic element of a error correcting code. To provide a potential avenue for extending monolithic chip-based architectures for quantum information processing, we employ the circuit elements of our architecture to implement a deterministic state transfer and entanglement generation protocol [1]. Our protocol is based on an all-microwave process, which entangles or transfers the state of a superconducting qubit with a time-symmetric itinerant single photon exchanged between individually packaged chips connected by a transmission line. We transfer qubit states at rates of 50 kHz, absorb photons at the receiving node with near unit probability, and achieve transfer process fidelities and on demand remote entanglement state fidelities of about 80 %. We also show that time bin encoding can be used to further improve these quantum communication metrics [5]. Sharing information coherently between physically separated chips in a network of quantum computing modules may be an essential element for realizing a viable extensible quantum information processing system.

[1] T. Walter et al., Phys. Rev. Applied 7, 054020 (2017) [2] P. Magnard et al., Phys. Rev. Lett. 121, 060502 (2018) [3] J. Heinsoo et al., Phys. Rev. Applied 10, 034040 (2018) [4] P. Kurpiers et al., Nature 558, 264-267 (2018) [5] P. Kurpiers et al., arXiv:1811.07604 (2018)

This research was performed in a collaboration between J.-C. Besse, A. Akin, S. Gasparinetti, J. Heinsoo, P. Kurpiers, P. Magnard, M. Pechal, B. Royer, Y. Salathe, S. Storz, T. Walter, A. Blais, C. Eichler, and A. Wallraff.

Manish Chhowalla (University of Cambridge, UK)

As the dimensions of semiconducting channels in field effect transistors (FETs) decrease, the contact resistance of metal-semiconductor interface at the source and drain electrodes dominates the performance. Two dimensional (2D) transitional metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) have been demonstrated to be excellent semi-conductors for ultra-thin FETs. However, unusually high contact resistance has been observed across the metal-2D TMD interface. We have shown that it is possible to reduce the contact resistance by forming lateral junctions between metallic and semiconducting phases of 2D materials. Recent studies have shown that van der Waals (vdW) contacts formed by graphene on 2D TMDs provide lowest contact resistance. However, vdW contacts between evaporated three-dimensional metal and 2D TMDs have yet to be demonstrated. Here, we report the realization of ultra-clean vdW contacts between 3D metals and single layer MoS2. Using scanning transmission electron microscopy (STEM) imaging, we show that the 3D metal and 2D MoS2 interface is atomically sharp with no detectable chemical interaction, suggesting van-der-Waals-type bonding between the metal and MoS2. We show that the contact resistance of indium electrodes is ~ 800 Ω-μm - amongst the lowest observed for metal electrodes on MoS2 and is translated into high performance FETs with mobility in excess of 160 cm2-V-s-1 at room temperature without encapsulation. We also demonstrate low contact resistance of 220 Ω-μm on 2D NbS2 and near ideal band offsets, indicative of defect free interfaces, in WS2 and WSe2. I will introduce 2D TMDs and their properties and then describe our efforts on making good contacts on 2D semiconductors.

Ali Yazdani (Princeton University, USA)

Ettore Majorana famously considered that there may be fermions in nature that are their own antiparticle — and then he mysteriously disappeared just after proposing the idea in 1938. In recent years, following pioneering theoretical work of Kitaev and others, we have learned how to engineer materials that harbor quasiparticles that behave similar to fermions Majorana had envisioned. In particular, there has been a focus on one-dimensional topological superconductor that harbor Majorana zero modes (MZM) that can potentially be used to make fault-tolerant topological quantum computation possible. Recently, we have proposed and implemented a platform for realization of topological superconductivity and MZM in chains of magnetic atoms on the surface of a superconductor [1,2]. In this talk, I will describe this platform and the series of experiments we have performed to establish the presence of these exotic quasi-particle using spectroscopic mapping with the scanning tunneling microscope (STM). [2-4] These include study of the unique spin signature of MZM.[4] Finally, if there is time I will discuss our most recent work on realization of MZM in a platform based on chiral quantum spin Hall edge states. Overall these experiments, illustrate how the power of spectroscopic imaging with the STM can be used to visualize novel quantum states of matter and their exotic quasi-particles.

[1] S. Nadj-Perge et al. PRB 88, 020407 (2013).
[2] S. Nadj-Perge et al. Science 346, 6209 (2014).
[3] B. E. Feldman et al. Nature Physics 13, 286 (2016).
[4] S. Jeon et al. Science 358, 772 (2017).

William J Munro (NTT Corporation, Japan)

Physics and information are intimately connected, and the ultimate information processing devices will be those that harness the principles of quantum mechanics. Many physical systems have been identified as candidates for quantum information processing, but none of them are immune from errors. The challenge remains to find a path from the experiments of today to a reliable and scalable quantum information processing devices. Here, we develop an architecture based on a simple module comprising an optical cavity containing a single negatively charged nitrogen vacancy center in diamond. Modules are connected by photons propagating in a fiber-optical network. We find that our architecture enables large-scale quantum information processing with existing technology.

Speaker: Prof Charles Bennett (IBM)

Time: 5pm on Monday 19th October

Location: Central Core of the Centre for Mathematical Sciences, Clarkson Road

Computation, Dynamics, Evidence, and Experience

Like other parts of mathematics, information and computation theory originated as abstractions of experience, but their 20th century founders left behind, as mere physics, important thermodynamic and quantum ideas whose subsequent incorporation has greatly enriched the mathematical theory.  Aside from its internal elegance, the new theory provides a deeper understanding of natural phenomena, such how thermodynamic disequilibrium enables the emergence of classical phenomenology from quantum laws, and the subsequent emergence of "logically deep" structures, containing internal evidence of a nontrivial history.

The workshop will take place at Murray Edwards College in Cambridge on September 11, 2015.

More information can be found at the conference website: http://siqip15.iopconfs.org/home

EPSRC Quantum Technologies Pump-Priming Collaboration Workshop is taking place on September 10, 2015 at the Cavendish Laboratory.

All funded researchers will be presenting their latest results and the schedule is as follows:

Agenda

1:30 pm  Welcome and introduction to the workshop – Mete Atature

A recap of the Quantum Cambridge Winter School 2015 – Aga Iwasiewicz-Wabnig

1:45 pm  Session 1 – short talks and discussion:  Chaired by Celestino Creatore

”Modelling quantum coherent electron systems” David Arvidsson Shukur

”InGaN quantum dots in GaN nanowires for polarisation controlled, wavelength multiplexed and electrically driven single-photon emitters” Lucy Goff

“Magnetic insulators for quantum inter-conversion” Stefan Lagenfeld

“Building collaborations: Exploring spin polarisation in graphene” David Love

“Topological Insulators: Synthesis of novel materials for quantum-enhanced devices” Angadjit Singh

“Building collaborations in quantum cryptography” Adrian Kent

2:45 pm  Coffee break

3:00 pmSession 2 – short talks and discussion: Chaired by David Love

”Two Dimensional Crystals for Quantum Science and Technology” Carmen Palacios-Berraquero and Matteo Barbone

“Long distance transport of qubits in silicon using surface acoustic waves” Tzu-Kan Hsiao

“A high-speed millikelvin nanopositioner for quantum readout of superconducting devices” Malcolm Connolly

“Exploring, controlling and exploiting quantum effects in biologically inspired DNA nanostructures” Celestino Creatore

“Single photon characteristics in hybrid quantum-classical photonic systems” Adrian Wonfor

4:00 pm  Closing remarks and further networking

http://www.jbs.cam.ac.uk/media/events/towngown-quantumcomputing/

21 April 2015 18:45-20:30

“Debate: This house believes that quantum computing, while scientifically interesting, will not make a practical difference to society in our lifetime”

Proposition: Dr Hermann Hauser, Co-Founder of Amadeus Capital Partners
Opposition: Ilyas Khan, Leader in Residence and Fellow in Management Practice, Cambridge Judge Business School and Aram Harrow, Assistant Professor of Physics, Massachusetts Institute of Technology

Town & Gown: Where Business & Academia Collide, a new series hosted by Cambridge Judge Business School, will bring the business and academic worlds together through thought-provoking debate. From technology to philosophy, topics will be addressed from academic and business viewpoints and you can expect to be challenged and stimulated by what you hear. Networking and drinks follow the debate where we encourage you to carry on the conversation.

A one-day workshop on quantum dots and confined systems in general is held in Cambridge on 12th January 2015. Details can be found here: http://www.amop.phy.cam.ac.uk/amop-ma/QDcam2015.pdf