Research

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Physics (R10 on the map)

Cavity QED with Cold Atoms

Cavity quantum electrodynamics is the study of how interactions between light and matter can be controlled by modifying the local environment. For example, optical cavities can be used to increase the intensity per photon and the effective lifetime, leading to strong coupling between single atoms and photons.

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High finesse ring cavity under ultrahigh vacuum
 

We have built an experiment to study gases of cold atoms in a high-finesse optical ring resonator. For large enough numbers of atoms (10s of thousands to millions), the coupling to the cavity field is both collective and coherent, overwhelming dissipation due to spontaneous emission and finite photon lifetime. In this regime, known as collective strong coupling, the atoms move according to the optical potential, and the optical potential responds to the positions of the atoms, leading to a rich nonlinear dynamics.

 

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Schematic of the ring cavity, with cold potassium atoms (green) overlapping the mode (red)
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Vacuum Rabi splitting with cold potassium atoms in a ring cavity.
 
 

Contact:
Dr Jon Golwin - contact

Quantum Optics and Photonics

We use 4-wave mixing in a rubidium vapour to generate beams that are entangled in their quadratures as well as in their transverse spatial degrees of freedom. These light fields, dubbed "quantum images", have subtle quantum correlations in their phases and their amplitudes that depend on the position in their transverse profiles. They could be used for the imaging of hard to see (transparent) objects, accurate beam positioning, or quantum cryptography.

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The level diagram of 85Rb, in (a), used to generate the probe (Pr) and conjugate (C) beams by four-wave-mixing process (4WM). The geometry of the nonlinear 4WM interaction, in (b), shows the generation of entangled images using a mask in the input probe beam.

 

We have recently generated squeezed light beam that displays noise lower than the shot noise in 75 independent regions or “locales” along its transverse profile [3]. This localised multi-spatial-mode (MSM) quadrature squeezing can be used to improve resolution of optical imaging

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The homodyne detection of the MSM quadrature squeezing works by scanning the position of the local oscillator (LO). This allows the mode structure mapping of the MSM squeezed vacuum.

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Observation of localised quadrature squeezing for two orthogonal scans of the LO positions (left and right). The squeezing as a function of the LO position is shown in (a) and (d) for two diameters of the LO beam, circles (narrower LO) and squares (wider LO). The images in (b) and (e) correspond to the squares and circles in the graph.

References:

  1. C. S. Embrey, J. Hordell , P. G. Petrov, and V. Boyer, Optics Express, 24, 27298–27308, (2016). doi:10.1364/OE.24.027298
  2. X. Zang, J. Yang, R. Faggiani, C. Gill, P. G. Petrov, J-P. Hugonin, K. Vynck, S. Bernon, P. Bouyer, V. Boyer, and P. Lalanne, Phys. Rev. Applied , 5, 024003, (2016). doi: 10.1103/PhysRevApplied.5.024003
  3. C. S. Embrey, M. T. Turnbull, P. G. Petrov, and V. Boyer, Phys. Rev. X, 5, 031004, (2015). doi:10.1103/PhysRevX.5.031004
  4. M. T. Turnbull, P. G. Petrov, C. S. Embrey, A. M. Marino, and V. Boyer, Phys. Rev. A, 88, 033845, (201doi: 10.1103/PhysRevA.88.033845
  5. A. M. Marino, R. C. Pooser, V. Boyer, and P. D. Lett, Nature 457, 859-862 (2009) doi:10.1038/nature07751;

Contact:
Dr Vincent Boyer - contact
Dr Plamen Petrov - contact

Ultracold Quantum Gases

In recent years the study of ultra-cold atomic gases has been one of the most flourishing fields in the international scientific scene. This is because the modern techniques of laser cooling and magnetic and optical trapping have made it possible to reach temperatures close to absolute zero in very dilute atomic samples. At such temperatures, the wave-like behaviour of matter clearly emerges and we can observe fascinating phenomena such as the Bose-Einstein condensation.

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Our Magneto-Optical trap of Rb atoms. The temperature of the atomic cloud in this picture is only ~0.0001 degrees above the absolute zero.

Bose-Einstein Condensates

The theoretical prediction of condensation dates back to 1925 when Bose and Einstein demonstrated that in a gas of identical non-interacting bosons, under a certain critical temperature, all the particles collapse into the same quantum state forming a new state of matter: the Bose-Einstein condensate, which has been first realized experimentally in 1995. Since then, this macroscopic object in which the undulatory character of matter can be easily observed has provided the Physics community with a new powerful tool for the investigation of the quantum properties of matter.

In the Ultracold Quantum Gases group we are able to produce Bose-Einstein condensates of Rb and ultracold mixtures of Rb and K atoms. We exploit the extraordinary properties of these exotic objects to study fascinating phenomena like the superfluidity, transport in non-linear media and the quantum magnetism.

Quantum simulations

One of the biggest challenges in modern Physics is the control, engineering and understanding of complex quantum systems. The main problem is represented by the fact that computation of large quantum systems can be practically impossible since the amount of resources necessary scales exponentially with the size of the system. A possible solution to this problem was given by Richard Feynman: to build a quantum simulator, i.e., a quantum machine that can reproduce, in a controlled environment, the quantum system under investigation. Indeed such a machine, being quantum by design, can handle an exponentially large amount of information without requesting an exponentially large amount of resources.
In the Ultracold Quantum gases group we are aiming at realizing Feynman's vision by using the high degree of control over our cold atoms to implement a quantum simulator. By using advanced techniques like the use of spatial light modulators and the control of inter-atomic interactions, we are able to implement a synthetic version of different systems, ranging from the photosynthesis process in biology to solid state devices like graphene and even neutron stars!

 

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Contact:
Dr Giovanni Barontini - contact

TTC (G6 on the map)

Atom Interferometry

Our research focuses on performing precision inertial sensing, and in particular on the measurement of gravity and gravity gradients, through atom interferometry. A large portion of our work involves bringing cold atom based gravity sensing to practical use, through improving the readiness, developing the underpinning hardware, and building demonstrators that can operate in application relevant environments – for example, targeting finding underground infrastructure using a cold atom gradiometer. We are the gravity sensing team of the UK National Quantum Technology Hub in Sensors and Metrology, and are leading in transferring knowledge and capability into industry to build up impact across a variety of potential end uses, such as within civil engineering or archaeology. Our work includes a variety of projects, ranging from those performing fundamental research aiming to improve the underpinning techniques to a cross-over between physics and engineering, and those in strong collaboration with industry.

Cold Atom Interferometry Group mini-site

Contact:

Prof. Kai Bongs - contact
Dr Michael Holynski - contact

Atom Clock

Contact:
Prof. Kai Bongs - contact
Dr Yeshpal Singh - contact