QUISCO are requesting expressions of interest from quantum information researchers in Scotland to join the management team, help organise events and co-ordinate local institutional activities. If you would like to be considered for these roles, please contact Elham Kashefi.

# QUISCO Meeting 7th November 2012 at Strathclyde

The next QUISCO meeting will be at the University of Strathclyde on the 7/11/2012 from 11am to 6pm. For directions to the university please see here. Links to campus maps are below.

Speakers include Dan Browne (UCL), Andreas Buchleitner (Freiburg), Jeremy O’Brien, (Bristol), Vedran Dunjko (Heriot-Watt), Daniel Oi (Strathclyde) and Raphael Dias Salva (Edinburgh).

There is no registration fee but in order to facilitate catering please send a message to quantumschmantum (this is AT google mail) in order to register.

The current schedule is as follows:

**Morning Session: JA325, John Anderson Building**

The best way into the building is either via the north facing side (which takes you into level 5, or by entering through the Colville building (building 20). Please see this campus map. The room is on level 3.

11.00am – 11.50am **Jeremy O’Brien** (University of Bristol)

“Photonic quantum technologies”

Abstract: “Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement, information and communication technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing, photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level. Encoding quantum information in photons is also an appealing approach to other quantum technologies, including quantum communication, metrology and measurement. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability. We have begun to address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised, and demonstrated Shor’s algorithm with consecutive CNOT gates and the iterative phase estimation algorithm. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly recongigurable quantum circuit able to perform almost any function on two photonic qubits, and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons. We have addressed miniaturisation using multimode interference coupler architectures to directly implement NxN Hadamard operations, and by using high refractive index contrast materials such as SiO_{x}N_{y}, in which we have implemented quantum walks of correlated photons, and Si, in which we have demonstrated generation of orbital angular momentum states of light. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light. We have begun to address the integration of superconducting single photon detectors and diamond and non-linear single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler’s delayed choice experiment.”

11.50am – 12.40pm **Vedran Dunjko** (University of Edinburgh)

“Universal Blind Quantum Computation with Weak Coherent Pulses”

Abstract: “The Universal Blind Quantum Computation (UBQC) protocol allows a client to perform quantum computation on a remote server. In an ideal setting, perfect privacy is guaranteed if the client is capable of producing specific, randomly chosen single qubit states. While from a theoretical point of view, this may constitute the lowest possible quantum requirement, from a pragmatic point of view, generation of such states to be sent along long distances can never be achieved perfectly. We introduce the concept of epsilon-blindness for UBQC, in analogy to the concept of epsilon-security developed for other cryptographic protocols, allowing us to characterize the robustness and security properties of the protocol under possible imperfections. We also present a remote blind single qubit preparation protocol with weak coherent pulses for the client to prepare, in a delegated fashion, quantum states arbitrarily close to perfect random single qubit states, allowing us to efficiently achieve $\epsilon$-blind UBQC for any epsilon>0, even if the channel between the client and the server is arbitrarily lossy. Time permitting, and conditional on the interests of the audience, additional topics related UBQC will also be discussed.”

12.40pm – 14.00pm **Lunch (location TBA)**

** **

**Afternoon Session: RC512, Royal College Building**

Please see this campus map for how to get to the building. The room is on level 5, but other than that there is limited logic to the room numbering, so please follow a local.

14.00pm -14.50pm **Andreas Buchleitner** (Universität Freiburg)

“Chaos and disorder for quantum control”

Abstract: “Quantum control is usually expected to be a delicate issue, based on carefully tuning system-specific parameters which then enforce that type of coherent quantum dynamics one is interested in. This in general implies fragile solutions, with respect to uncontrolled perturbations or imprecisions. An alternative route consists in using the eigenstates of complex quantum systems as carriers of robust control. The lecture will present concrete examples which underpin this latter perspective, and discuss possible experimental implementations.”

14.50pm -15.40pm **Daniel Oi** (University of Strathclyde)

“Measuring Nothing”

Abstract: “Non-destructive measurements of the optical field are important for a host of applications in communication, state preparation, and they also give us new tools to probe its quantum nature. Here, we describe a novel type of measurement which implements the ideal projection onto the vacuum or its complement, i.e. not vacuum, but preserving the ideal state in the latter case. For the not-vacuum result, this requires the measurement to obtain no information of the photon number distribution (other than it is greater than zero) even in principle. Conventional approaches suffer from a square root dependence of the coupling to a probe on photon number, hence leading to non-ideal dynamics. Here, we show how an adiabatic transition overcomes this photon number dependence and leads to the unusual non-linearity required. We propose experimental implementations which should be technically feasible given state of art the parameters and simulate the performance of the technique in the presence of decoherence.”

15.40pm – 16.10pm **Coffee Break (location TBA)**

16.10pm – 17.00pm **Daniel Browne** (University College London)

“Qudit magic state distillation”

Abstract: “Magic state distillation is an important technique in fault tolerant quantum computation, enabling universal quantum computation with fault tolerant Clifford group gates. In my talk, I will show how it can be generalised to qudits, and that this forces us to answer lots of fundamental questions about qudit quantum computation which surprisingly had not been addressed before – such as what makes a universal set of qudit gates?”

17.00pm – 17.50pm **Raphael Dias Silva **(Universidade Federal Fiuminense/University of Edinburgh)

“Compact quantum circuits from one-way quantum computation”

Abstract: “In this talk I will introduce a new method to translate measurement patterns to the circuit model and discuss some applications of it. We start by giving a straightforward circuit representation of any 1WQC, at the cost of introducing many ancilla wires. We then propose a set of four simple circuit identities that explore the relationship between the entanglement resource and correction structure of a 1WQC, allowing one to obtain equivalent circuits acting on fewer qubits. In the second part of the talk, I will show how to optimize arbitrary quantum circuits by using back-and-forth translation between the QC and 1WQC models.”

# Scott Aaronson Distinguished Lecture at the Informatics Forum

Friday, 13 July 2012, 4:00 pm

Room G.07, School of Informatics

10 Crichton Street, Edinburgh EH8 9AB

and afterwards for a drinks and canapé reception

### Quantum Computing and the Limits of the Efficiently Computable

I’ll discuss what can and can’t be feasibly computed according to physical law. I’ll argue that this is a fundamental question, not only for mathematics and computer science, but also for physics; and that the infeasibility of certain computational problems (such as NP-complete problems) could plausibly be taken as a physical principle, analogous to the Second Law or the impossibility of superluminal signalling. I’ll first explain the basics of computational complexity, including the infamous P versus NP problem and the Extended Church-Turing Thesis. Then I’ll discuss quantum computers: what they are, whether they can be scalably built, and what’s known today about their capabilities and limitations.

Lastly, I’ll touch on speculative models of computation that would go even beyond quantum computers, using (for example) closed timelike curves or nonlinearities in the Schrodinger equation. I’ll emphasize that, even if “intractable” computations occur in a particular description of a physical system, what really matters is whether those computations have observable consequences.

# Scott Aaronson Talk Schedule

Venue: School of Informatics, University of Edinburgh, Room 4.33/4.31

Times: 15:00 till 16:30

**New Computational Insights from Quantum Optics**

Tuesday 10/7/2012

In work with Aleksandr Arkhipov, we proposed a rudimentary form of quantum computing, based on linear optics with nonadaptive measurements; and used a connection between linear optics and the permanent function to show that even this limited model could solve sampling and search problems that are intractable for classical computers under plausible complexity assumptions. In this talk, I’ll discuss this work in a self-contained way, and mention some of its implications for quantum computing experiments. I’ll also discuss some more general results that emerged from our work. These include a new equivalence between sampling problems and search problems based on Kolmogorov complexity; a new, linear-optics-based proof of Valiant’s famous theorem that the permanent is #P-complete; and a new classical approximation algorithm for the permanent.

Papers:

The Computational Complexity of Linear Optics

The Equivalence of Sampling and Searching

A Linear-Optical Proof that the Permanent is #P-Hard

**How Much Information Is In A Quantum State?**

Wednesday 11/7/2012

People often talk about the quantum state of n entangled particles as if it contained an amount of information exponential in n. In this talk, I’ll discuss three results that suggest that, in various senses relevant for computation, prediction, and learning, quantum states

actually *don’t* behave as if they contained exponential amounts of information. Specifically, I’ll discuss the limitations of “quantum advice states,”the approximate “learnability” of quantum states from random measurement results, and the simulation of arbitrary quantum state preparation tasks by the preparation of ground states of local Hamiltonians (joint work with Andrew Drucker).

Papers:

Limitations of Quantum Advice and One-Way Communication

The Learnability of Quantum States

A Full Characterization of Quantum Advice

**Talk #3**

Thursday 12/7/2012

Talk #3 will be determined based on audience interest.

# Scott Aaronson Visits QUISCO

We’re delighted to announce that Prof. Aaronson will be visiting us from July 9 till July 13 and will present a series of lectures on quantum complexity theory covering topics on complexity of linear optics and information content of quantum states.

The venue is the School of Informatics, University of Edinburgh, Room 4.33/4.31 on Tuesday, Wednesday and Thursday July 10, 11 and 12 from 15:00 till 16:30.

We hope you can all attend this unique rejuvenating QUISCO meetings.

**Biography**

Scott Aaronson is an Associate Professor of Electrical Engineering and Computer Science at MIT. He received his PhD in computer science from University of California, Berkeley and did postdocs at the Institute for Advanced Study and the University of Waterloo. Scott’s research interests center around fundamental limits on what can efficiently be computed in the physical world. This has entailed studying quantum computing, the most powerful model of computation we have based on known physical theory. He also writes a popular blog, and is the creator of the Complexity Zoo, an online encyclopedia of computational complexity theory. He is the recipient of NSF’s Alan T. Waterman Award for 2012.

I'm delighted to announce that Prof. Aaronson will be visiting us from July 9 till July 13 and will present a series of lectures on quantum complexity theory covering topics on complexity of linear optics and information content of quantum states. The venue is the School of Informatics, University of Edinburgh, Room 3.44 on Tuesday, Wednesday and Thursday July 10, 11 and 12 from 15:00 till 16:30. I hope you can all attend this unique rejuvenating QUISCO meetings, Elham BIO Scott Aaronson is an Associate Professor of Electrical Engineering and Computer Science at MIT. He received his PhD in computer science from University of California, Berkeley and did postdocs at the Institute for Advanced Study and the University of Waterloo. Scott's research interests center around fundamental limits on what can efficiently be computed in the physical world. This has entailed studying quantum computing, the most powerful model of computation we have based on known physical theory. He also writes a popular blog<http://(www.scottaaronson.com/blog)>, and is the creator of the Complexity Zoo <http://(www.complexityzoo.com)>, an online encyclopedia of computational complexity theory. He is the recipient of NSF's Alan T. Waterman Award<http://web.mit.edu/newsoffice/2012/aaronson-nsf-award-0308.html>for 2012.

# Wednesday 30/11/2011 Talks, Edinburgh Informatics Forum

## A glance of blind computing

### Vedran Dunjko

### 13:30, IF 4.02

**Abstract:** In 1978, Rivest et al. have, by asking “Is computation over data which has been encrypted possible?”, opened up a proliferate area of research in cryptography. The following 30 years yielded partial results in both the classical and new domain of quantum computation: Feigenbaum et al (1989) showed that classical computation with unconditional privacy of an NP-hard function is impossible (unless PH collapses to the 3rd level) and Childs (2005) and later Aharonov et. al, reflected on this problem in the quantum domain with only partial success. Then, 2009. saw breakthroughs in both settings: Gentry offered a positive answer in terms of a classical efficient fully homomorphic encryption, and Boradbent, Fitzsimmons and Kashefi presented the Universal Blind Quantum Computation (UBQC) protocol. Gentry’s classical scheme offers computational security whereas the UBQC scheme is unconditionally secure, but the user needs modest quantum powers. In this talk we will note the highlights of the turbulent history of computation with encrypted data, address the interplay between classical and quantum results, and their impact on cryptography, interactive proof systems and the understanding of the separation between “classical” and “quantum” in information processing. Finally, we will briefly go through the details of the UBQC protocol, and provide alternative proofs of its security.

## The ZX-Calculus: a graphical approach to quantum computing

### Ross Duncan

### 4pm, IF 4.31-33

**Abstract:** The ZX-calculus is a graphical notation for quantum computing based on monoidal categories and the physical notion of “strong complementarity”. In this talk I’ll explain what string complementarity is, and introduce the ZX-calculus. I’ll also demonstrate some recent applications of the calculus to problems in and around quantum computing.

# Wine and Cheese Event 2/12/2011

Dear QUISCO members, QUISCO-philles and associated wonderful people,

It is our pleasure to invite you to the very first QUISCO Wine and Cheese Event, on Friday, 2nd December 2011, at University of Edinburgh’s **Informatics Forum**. The Event will commence at 5pm at the 4th floor miniforum. Kids, partners, friends are most welcome to join!

**Mission and vision:** The idea is to institutionalise this event every first Friday of the month, where quantum and non-quantum people can socialize, discuss, and enjoy great wine and cheese in a very informal friendly atmosphere:

Students: you get to bug your supervisors

Supervisors: you get to converse your students

Researchers in general: mingle, discuss, expand your interests and start new collaborations!

During the course of the first event we will also brainstorm a bit about the actual format of the Events to come, based on the heart’s desires of the attendees.

For the reasons of simplicity, for the first Event, it is a BYOB & C festivity: contribute with a bottle of wine or juice, and ofc. cheese if you can. Please do us the honor and join us to make this fun idea a success!!

For any additional information feel free to contact me at the following e-mail address and cell phone number:

email: vd51 (at) hw ac uk

cell: +44 7907 980 936

Hope to see you soon!

Kind Regards,

Vedran Dunjko

p.s. If you choose to join us at a later stage of the event, please keep my number

# Anton Zeilinger Talk at Heriot-Watt 23/11/2011

### Quantum Games, Quantum Information, and the Foundations of Quantum Physics

Prof. Anton Zelinger

University of Vienna

Physics Colloquium

Wed 23 November – 2:30pm

Postgraduate Centre Auditorium

Heriot-Watt University

For more details, contact:

Dr E Abraham

E.Abraham@hw.ac.uk

# New Student Representative

We welcome Electra Eleftheriadou as a student representative for Strathclyde. We are on the lookout for other students representatives and we are not restricted to only one per site.

Daniel.

# New QUISCO Site

We’re moving the old QUISCO website to this new version. Please bear with us till we have transferred all the material over.

Daniel Oi,

QUISCO Dogsbody.