Durham Atomic and Molecular Physics: Part of the JQC Durham–Newcastle 
AtMol Research Seminars

Date  Speaker  Institution 

Quantum Computation by Shaking Lattices — Journal Club Talk  
10th Oct  Mr. Tom Ogden  Durham University 
I'll talk about a scheme for quantum computation in optical lattices, proposed recently by PhilippImmanuel Schneider and Alejandro Saenz at HumboldtUniversität zu Berlin. The idea is that qubits are encoded in the spatial wavefunction of the atoms, and operations are performed by shaking the lattice. I'll discuss the theoretical model and their numerical predictions of fidelity and gate times. 

Highly polarized limit of the quasi2D Fermi gas  
17th Oct  Dr. Jesper Levinsen  University of Cambridge 
An ultracold gas of fermionic atoms with short range interactions represents a unique playground for studying pairing and effective interactions in a strongly correlated system due to the fine control of dimensionality and interactions. In this talk, I will start by reviewing recent theoretical and experimental progress in the field. Focussing next on the highly polarized limit of the quasi2D Fermi gas, I will discuss properties of the quasiparticles which a single impurity can form when immersed in a Fermi sea. I will show how the ground state transition of the attractive branch is shifted by the quasi2D confinement and how this can be described quantitatively throughout the 2D to 3D crossover. I will also demonstrate how the fast decay of the repulsive branch precludes itinerant ferromagnetism in this system. 

Superfluids and Superconductors with Spin Triplet Cooper pairing  
24th Oct at 13.00  Prof. James Annett  University of Bristol 
In most known superconductors the Cooper pairs of electrons form into S=0 spin singlet pairs. However a much more rich set of phenomena can occur in the case of S=1 spin triplet pairing. Such a pairing state was first realized in superfluid helium3 at 2.2mK. However there is now strong evidence for triplet superconductivity in a number of different materials. Perhaps the best evidence is in the material Sr2RuO4, which is superconducting below 1.5K. The pairing state in this system appears to be chiral, breaking time reversal symmetry. We discuss the intrinsic magnetism arising from this chiral state, and its relationship to the controversial spontaneous condensate angular momentum expected in superfluid helium3. Another class of materials where triplet pairing may occur are crystals without a centre of inversion symmetry. Finally it is also possible to create spin triplet pairs in artificial multilayer systems which combine ferromagnetic and conventional singlet superconductors. 

Optomechanics with levitated microspheres  
31st Oct  Dr. James Millen  University College London 
The field of optomechanics is the study of the interaction of light with the bulk mechanical motion of macroscopic objects. The goal is to use light to cool the centreofmass motion of an oscillator to the subphonon level, at which point the oscillator will be in a quantum state. Several groups have managed to cool micron sized objects to this c. o. m. motional quantum ground state [13], though quantum effects are difficult to observe due to extremely rapid decoherence mechanisms, mainly due to thermal excitation. Recent theoretical work has suggested that by levitating the oscillator one can isolate it from sources of decoherence, prepare it in Gaussian state, drop it and produce a quantum superposition of a macroscopic object (containing ~1018 atoms) [4]. Our group has studied methods of cooling glass nano and microspheres, using optical cavities [57] and whispering gallery mode resonances [8]. We are also using the levitated microsphere system to study nonequilibrium thermodynamics, a surprisingly fledgling field of research that has begun to experimentally verify deep relationships between energy and information [9], and the relevance of the thermodynamic laws on the microscale [10].


Photonic Qubits, Qutrits and Ququads in Linear Optical Quantum Circuits  
7th Nov  Dr. Axel Kuhn  University of Oxford 
The ability of encoding arbitrary information in elementary quantum systems is the key to a novel approach to computing based on quantum mechanics. Particular attention has been paid toward the field of linear optics quantum computing (LOQC) which in principle is a scalable, albeit often restricted by the spontaneous nature of parametric downconversion sources. Here, I will show that single photons emitted on demand from a single atom into an optical cavity can be used to get past those limits. With a coherence time greater than 500 ns, a subdivision of photons into d time bins of arbitrary amplitudes and phases has been achieved, which we use for encoding arbitrary qudits in one single photon. The fidelity of the quantum state preparation is verified in timeresolved quantumhomodyne measurements, and the photons are used to operate elementary quantum gates in integrated photonic circuits. 

Journal Club Talk — Optical Determination of Boltzmann’s Constant  
14th Nov  Mr. Mark Zentile  Durham University 
Boltzmann’s constant is our link between the macroscopic world of bulk objects and the microscopic world of atoms and molecules. In this journal club talk I will explain what Boltzmann’s constant is and why we want to determine it accurately. Recently, new experimental techniques have been developed to measure Boltzmann’s constant by measuring the Doppler broadening of lineshapes in laser absorption spectroscopy. I will explain these experimental techniques and also refined theoretical models for lineshapes which must be applied for these precision measurements. 

Experiments with cold trapped Rydberg atoms and molecules  
21st Nov  Dr. Stephen Hogan  University College London 
The recent development of methods to manipulate the translational motion of atoms and molecules in Rydberg states, using inhomogeneous electric fields, has led to the realisation of Rydberg atom and molecule optics elements which include mirrors [1], lenses [2] and traps [35]. These devices have applications in (i) the development of hybrid approaches to quantum information processing involving Rydberg atoms and microwave circuits [6], (ii) the preparation of gasphase molecular samples at temperatures below 1 K [7], for studies of slow decay processes and lowenergy scattering, and (iii) the confinement and manipulation of antihydrogen atoms [8]. In this talk I will describe experiments with electrostatically trapped hydrogen atoms and hydrogen molecules, with an emphasis on the role of radiative processes in the decay of the trapped samples.


Interfacing cold atoms and superconductors  
28th Nov  Prof. Dr. Jozsef Fortagh  University of Tuebingen 
The goal of our experimental research is the realization of hybrid quantum systems based on cold atoms and solids. I will report on coherent manipulation of atoms near superconducting nano structures and will present data on the interaction between atoms and carbon nanotubes. 

Stirring up entanglement: quantum metrology with rotating matter waves  
5th Dec  Dr. Jacob Dunningham  University of Leeds 
Quantum metrology makes use of entanglement to achieve measurement precisions beyond what could be achieved by conventional classical methods and is rapidly emerging as an exciting and feasible new technology. I will give a brief introduction to the field before focusing on the particular case of atomic BoseEinstein condensates (BECs) trapped in rotating potentials. These are appealing because they are within reach of current experiments, provide a conceptually simple way of generating manybody entanglement, and have the prospect of leading to the development of ultraprecise gyroscopes. In order to employ such a system for metrology, it is important to understand the detailed form of the entangled states that can be created. I will present a study that goes beyond the Landau level (LLL) approximation. I will demonstrate that whilst the LLL can identify reasonably the critical frequency for a quantum phase transition and entangled state generation, it is vital to go beyond the LLL to identify the details of the state and quantify the quantum Fisher information (which bounds the accuracy of the phase measurement). We thus identify a new parameter regime for entangled state generation, amenable to experimental investigation. 

Rochester Lecture. Place and time to be confirmed.  
12th Dec  Dr. Alain Aspect  CNRS 

Department of Physics, Durham University  Tel +44 (0)191 33 43520 
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