## Imperial College London quantum optics and laser group

## Quantum Computers

A quantum computer represents, possibly, the ultimate form of quantum technology. The idea was born from various reasonings. The operation of a quantum computer is totally different from that of a conventional computer. While in the latter, information is represented by a definite number encoded on a string of 1s and 0s, a quantum computer allows the information to exist in a superposition of more than one state. This massive parallelism is one of the keys to the quantum speedup. However, there is an important rule in quantum mechanics which seems to deny this advantage – only one outcome can be obtained after the whole process. Thus, in order to utilise the massive parallelism provided by the quantum computer, algorithm should be developed carefully, taking the reality of the measurements in mind.

We provide PhD projects in relation to the hardware development of basic units of a quantum computer based on ions, atoms, photons and molecules. Our projects also include quantum simulations.

### Imperial College London quantum optics and laser group

## Quantum Information

This is an optional course taken from the final year Physics Undergraduate course. A summary is given in the current MSc Handbook. Other documents for this course (example sheets etc) are stored on Blackboard. The list below is indicative of the type of material covered in this course (taken from the 2015-16 course).

**Mathematical foundations of QI**

No cloning theorem, pure states, mixed states etc, generalized measurements, general evolution under completely positive maps.

**Quantum communication**

Teleportation/dense coding, Bell inequalities, generic properties of two-party pure state entanglement, entanglement as a powerful and interesting resource, elements of classical information theory, von Neumann entropy, Schumacher coding, information transmission channels

**Entanglement Theory**

Basic properties of entanglement: characterization/verification, manipulation (mixed state entanglement, distillation) and quantification

**Quantum computer science**

Notions of computational efficiency, classical and quantum gates and circuits, Examples of quantum gate implementations in ion traps, cavity QED, photons. Quantum algorithms: Deutsch/Jozsa algorithm, Grover’s algorithm

**Building a quantum computer**

Di Vincenzo criteria and critical analysis of the general requirements for the realization of QIP, Analysis of 2 promising architectures (e.g: ion traps, linear optics, superconducting qubits, quantum dots, spin chains,…)

**Quantum Error Correction**

Error correcting codes, how finite fault tolerant thresholds arise

## Course material

Course worksheets from the 2015-16 course and other useful information such as past exams can be found at:

### Imperial College London quantum optics and laser group

## Controlled Quantum Dynamics

The research interest of the group is the control and manipulation of physical systems to exhibit manifestly quantum mechanical effects such as quantum correlations and quantum interference. The emphasis is on using these effects to perform novel protocols in e.g. quantum computing or communication or to uncover the subtle role quantum mechanics may play in natural phenomena. This often involves theoretical and experimental approaches that allow us to work directly with individual quantum systems. In other cases the quantum dynamics of the systems may be under exquisite experimental control but an ensemble of systems may be used for enhanced read-out. The quantum simulation of many-body quantum systems is one aspect of our focus – it is a topic of crucial importance in fields ranging from quantum chemistry and biochemistry to the study of exotic materials such as graphene, high-temperature superconductors and carbon nanostructures. Another key area is the enhancement of metrology (high precision measurement) using entanglement as a resource. Our general approaches can also be used, for instance, to elucidate the role of fundamental symmetries in nature. Finally, the study of controlled quantum dynamics may lead us to new insights in the foundations of quantum mechanics itself.

Interested in doing a PhD in quantum information theory, foundations of quantum mechanics or other areas of controlled quantum dynamics? Then consider applying to our Centre for Doctoral Training in Controlled Quantum Dynamics.

### Imperial College London quantum optics and laser group

We are delighted to announce that Professor Richard Thompson has been appointed as the new Head of the Quantum Optics and Laser Science Group succeeding Professor Jon Marangos with immediate effect.

Please join us in congratulating Richard and in thanking Jon for his many contributions in this role over the last five years.