Quantum fluids

Quantum phenomena are at the heart of the upcoming technological wave that is going to power a new generation of smart materials and devices.

Computers with “classical” hardware are not suitable and overburdened with the simulation of large quantum mechanical systems because the size of the Hilbert space is growing exponentially.

As envisaged by Richard Feynman, quantum simulators could fill this gap, where another well-controlled and measurable system can be used to efficiently mimic and explore the physics of the otherwise inaccessible and intractable systems.

We aim to real­ize a scal­able, easy-to-han­dle de­vice plat­form based on po­lar­i­ton quan­tum flu­ids able to sim­u­late such sys­tems.

—IBM scientist Thilo Stöferle

In particular, phenomena like strongly correlated and topological phases that are key to both fundamental and exotic material features such as superconductivity and the spin Hall effect are notoriously difficult to tackle experimentally and theoretically [1].

Although very elaborate experiments with ultracold atoms at nano-Kelvin temperatures have provided a glimpse of the potential of a quantum simulator [2], an approach which is much less complex and suitable to become an integrable, widely-usable technology is still missing. Compelling candidates are Bose–Einstein condensates (BEC) of exciton polaritons, which are macroscopically coherent matter waves of quasi-particles built from electron-hole pairs (excitons) and photons [3].

Ask the experts

Thilo Stöferle

Thilo Stöferle

IBM Research scientist

Rainer Mahrt

Rainer Mahrt

IBM Research scientist

Building on our recent demonstration of non-equilibrium BEC of exciton polaritons with an amorphous polymer at room temperature [4], we are creating photonic potential landscapes for polariton condensates by harnessing novel nanostructured, tunable cavity arrays [5].

Furthermore, the same platform allows us to make use of colloidal semiconductor nanoplatelets and perovskite nanocrystals [6]to reach into the regime of strong interactions.

These new classes of materials implement the ideal compromise between high overall oscillator strength and strong exciton confinement, while at the same time offering advanced assembly options that allow us to form regular arrays.

These experiments could enable access to strongly correlated phenomena such as a quantum phase transition to a Mott insulator [7,8], which has been elusive to polariton systems up to now.

The polariton condensate appears as a nonlinearly growing peak in the momentum distribution

Polariton condensate

The polariton condensate appears as a nonlinearly growing peak in the momentum distribution, corresponding to the macroscopic population of the state.

Interference fringes in a Michelson interferometer are a signature of the long-range spatial coherence.

Pinned vortices result in fork-like dislocations.

A wavelength-scale Gaussian-shaped deformation

Wavelength-scale Gaussian-shaped deformation

The pattern on the left is achieved by focused ion beam milling into the substrate.

Atomic force microscopy (center) reveals the smooth Gaussian structure on the top mirror substrate.

By mounting both halves of the optical microcavity on XYZ-nanopositioners, we create tunable polaritons in the external potential given by the nanostructure.

References

[1] I. Buluta, F. Nori,
Quantum Simulators,”
Science 326, 108 (2009).

[2] I. Bloch, J. Dalibard, S. Nascimbène,
Quantum simulations with ultracold quantum gases,”
Nature Physics
8, 267 (2012).

[3] T. Byrnes, N. Y. Kim, Y. Yamamoto,
Exciton–polariton condensates,”
Nature Physics
10, 803 (2014).

[4] J. D. Plumhof, T. Stöferle, L. Mai, U. Scherf, R.F. Mahrt,
Room-temperature Bose-Einstein condensation of cavity exciton-polaritons in a polymer,”
Nature Materials
13, 247 (2014).

[5] D. Urbonas, T. Stöferle, F. Scafirimuto, U. Scherf, R.F. Mahrt,
Zero-Dimensional Organic Exciton–Polaritons in Tunable Coupled Gaussian Defect Microcavities at Room Temperature,”
ACS Photonics 3, 1542 (2016).

[6] G. Rainò, G. Nedelcu, L. Protesescu, M.I. Bodnarchuk., M.V. Kovalenko, R.F. Mahrt, T. Stöferle,
Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking, and Exciton Fine Structure,”
ACS Nano 10, 2485 (2016).

[7] M.J. Hartmann, F.G.S.L. Brandão, M.B, Plenio,
Strongly interacting polaritons in coupled arrays of cavities,”
Nature Physics 2, 849 (2006).

[8] A.D. Greentree, C. Tahan, J.H. Cole, L.C.L. Hollenberg,
Quantum phase transitions of light,”
Nature Physics 2, 866 (2006).