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NanoPhotonics Centre

 
Theoretical oscillations in a semiconductor microcavity

An overview of the group's research into microcavities.

Semiconductor microcavities are solid state devices that display quantum phases of strongly coupled light and matter

Microcavities are wavelength-sized optical cavities that trap light at specific wavelengths. This confinement allows photons trapped in the microcavity to strongly interact with matter, creating new quasiparticles called polaritons. Polaritons are a mixture of photons and semiconductor excitons that display different properties from either the light or matter that composes them.
Our current work concentrates on the creation and control of polariton quantum condensates.

 

Current Work

Spin bifurcation

Spin symmetry breaking and lattices

Using multiple laser spots to inject polaritons allows us to controllably create trapped polariton condensates. We have demonstrated how single trapped condensates display new spin dynamics with a symmetry breaking transition, and we have demonstrated our ability to controllably couple two of these trapped condensates. These are the first steps towards optically created large arrays of interacting quantum condensates.

 

Key papers:

MesaElectrical Control

By building semiconductor microcavities across which we can apply a voltage, polaritons can be polarised. This means that the electron and hole pairs which make them up are separated to opposite sides of the thin layers in which they are formed. This can make extremely fast electrically-controlled optical amplifiers as well as spin switches.

 

Key papers: 

  1. Dreismann, A. et al. Nature Mat. (2016).
  2. Cristofolini, P. et al. Science 336, 704 (2012).

Polariton Condensate Locking and TrappingPolariton condensate locking and trapping
In extraordinarily high quality samples, polaritons move freely. Injecting several condensates at once using multiple optical spots on the sample, allows us to watch how they interact. The polariton condensates like to phase lock stably over many minutes. Polaritons are trapped in between, oscillating back and forth spontaneously. New experiments show our ability to trap, sculpt, and control the polaritons with over 20 reconfigurable condensates injected.

Key papers:

  1. Tosi, G. et al. Nat Phys 8, 190 (2012).
  2. Tosi, G. et al. Nat. Comm. 3, 1243 (2012).
  3. Cristofolini, P. et al. Phys. Rev. Lett. 110, 186403 (2013).
  4. Dreismann, A. et al. PNAS 111, 8770 (2014).
 

Past Work

Room Temperature Polariton CondensatesRoom temperature polariton condensates
We demonstrated the first polariton BEC at room temperature using GaN based semiconductors.

Key paper: Christopoulos, S. et al. Phys. Rev. Lett. 98, 126405 (2007).

Room Temperature Polariton MEMSRoom temperature polariton MEMS
Using semiconductor layers with air gaps etched in between, we created room temperature semiconductor microcavities which can be bent using applied voltage or vibrated, to form opto-mechanical exciton-photon devices.

Key paper: Grossmann, C. et al. App. Phys. Lett. 98, 231105 (2011).

Optically-Spaced Quantum WellsOptically-spaced quantum wells
Instead of making a cavity, we unfolded it by making a stack of semiconductor quantum well emitters which were spaced a quarter optical wavelength apart. These interact with each other, emitting and absorbing photons, making a new strong-coupled state called a Bragg polariton.

Key paper: Askitopoulos, A. et al. Phys. Rev. Lett. 106, 76401 (2011).

Stimulated ScatteringStimulated scattering
Another peculiarity of polaritons in such strong-coupled semiconductor microcavities is that polaritons can collide with each other very efficiently. We discovered in 2000 that when light is injected at a very specific angle, the polariton scattering efficiency becomes enormous, making possible all-optical switches and the kick-starting the now-expanding science and technology of polaritonics. The optical gain (or amplification per unit length) in these devices is larger than in any other material ever produced.

Key paper: Savvidis, P. G. et al. Phys. Rev. Lett. 84, 1547 (2000).

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