Testing the quantum superposition principle 1

Motivation: Test Collapse models Collapse models: CSL, GRW, Schroedinger-Newton, Diosi-Penrose, …

What system parameters do we need to generate macroscopic Quantumness? Large mass Larger spatial separation/ size of superposition state Large time for the superposition state to exist

Macroscopicity measure: to compare different experiments and to check if they test the superposition principle and CSL models

MOLECULE INTERFROMETRY Scaling mass in matter-wave interferometry …

Mass record in matter-wave interferometry, 2013, Vienna: 10,000amu Kapitza-Dirac Talbot-Lau Interferometer

Set up of vertical interferometer in Southampton: Van der Waals/Casimir Polder interactions Wigner function reconstruction Spin effects Talbot-Lau Interferometer 7 Settings: mbar base pressure Water cooled Knudsen source In-situ grating alignment & positioning TOF scheme 3 rd grating position (µm) Count rate (cps) First signs of life! Time-of Flight modification

Measuring and using the spin of matter- waves Step 1) Adding magnetic field to the TLI Step 2) removing TLI -> pure magnetic manipulation Matter-wave Stern-Gerlach Matter-wave Rabi RF deflection

NANOPARTICLE INTERFEROMETRY Scaling mass even further … good for gravity sensing (decoherence and dephasing) … technologies much simpler than for molecules

Scheme: Matter-wave interferometry of 10 nm sphere Talbot interference of mass: 10 6 amu Wigner function model of interference pattern with all known dephasing and decoherence effects. Dominating decoherence effect: Thermal photo-emission. Mass of particle is limited by Earth’s gravity … future experiment in space Based on existing techniques! Bateman, J., S. Nimmrichter, K. Hornberger, and H. Ulbricht Near-field interferometry of a free-falling nanoparticle from a point-like source arXiv: (2013). Setup: Quantum carpet:

Experiments with nanoparticles: the particle optical trap (single site trap) Trap with 1550 nm laser to reduce absorption/heating effects Use of reflective optics to form trap, to avoid lens errors and chromatic effects and for high NA Setup schematics:Particle in the trap: 100 nm polystyrene, ~ 1 W, NA=0.9, 1 mbar Next steps: Feedback cooling (fast FPGA electronics for feedback), 10 mK com motion, 3 d, … then evacuate (10 -9 mbar), then do with 10 nm particle, … then interferometry. Mechanical frequency measurement:

See the mechanical oscillation ….

Experiments with nanoparticles: In-situ particle source (laser ablation of Si nanoparticles) Frequency Doubled YAG, 5 ns at 10Hz. Pulse power of 250 mW Initially trapped with 5 W at atmosphere, standing wave trap Pumped down slowly to 0.5 mbar Lowest trapping power at 2.5 W

MAQRO Consortium of 40 scientists from all over the world Planned application for a M4 class mission in 2014 It is to bring our nanoparticle interferometer into space! Nanoparticle interferometer in space to control influence of gravitation, it is impossible on Earth above a certain mass

THE MATTER-WAVE TO OPTO- MECHANICS INTERFACE To scale mass even further …. (10 13 amu)

How to go bigger?: Transfer superposition state! All parts of this proposal are based on existing, demonstrated technology Macroscopicity of 30 (Nimmrichter macroscopicity) Scheme for experiment (matter-wave->mechanics->optics): Spatial superposition state of atomic He + is incident to a pair of mirrors Mirrors are coupled to light in cavity Read-out of light field by state tomography by pulsed opto-mechanics scheme Xuereb, A., H. Ulbricht, and M. Paternostro, Optomechanical interface for matter-wave interferometry, Scientific Reports 3, 3378 (2013). Optics is coupling the motional state of the two ‘initially’ independent opto-mechanical systems., generating a joint motional state. All individual (solid-state) effects in each optomechanical System is erased – and the spatial information about them is lost, Then the particle hit …. Faster than decoherence! Time- scales involved:

Theoretical analysis: Number state for incoming particle in superposition Thermal state for both opto-mechanical systems (no ground state needed!, state can be different for both) Definition of joint motional state of opto-mechanics Negativity of Wigner function of the joint mechanical state by state tomography (as by pulsed optomechanics) Xuereb, A., H. Ulbricht, and M. Paternostro, Optomechanical interface for matter-wave interferometry, Scientific Reports 3, 3378 (2013). Result: Superposition state survives transfer!

Study the system: Look into a definition of macroscopicity of this specific system treatment of decoherence … Macroscopicity depending on generic decoherence Macroscopicity of our system A. Xuereb, H. U., M. Paternostro, Macroscopicity in an optomechanical matter-wave interfrometer, submitted (2014).

DIFFERENT APPROACH: FREQUENCY DOMAIN TESTS

Generic broadening of spectral linewidth from collapse (noise): Bahrami, M., A. Bassi, and H. Ulbricht Testing the quantum superposition principle in the frequency domain arXiv: (2013). [accepted for publ. in Phys. Rev. A]

Applied to opto-mechanical system Collapse noise affects mechanical motion of opto-mechanical system, read out by optics Broadening effect modeled by input/output theory of opto-mechanics. Factor of 5 effect for cooled mechanics predicted for realistic experimental conditions to test Adler CSL. M. Bahrami, M. Paternostro, A. Bassi and H. Ulbricht Non-interferometric Test of Collapse Models in Optomechanical Systems, arXive: (2014).

Thanks to …. Group at Southampton: James Bateman, Nathan Cooper, Muddassar Rashid, David Hempston, Jamie Vovrosh. Quantum Optics theory: Mauro Paternostro, Andre Xuereb, Matter-wave interferometry and experiments: Peter Barker, Markus Arndt, Klaus Hornberger, Stefan Nimmrichter, MAQRO consortium Foundations of Physics: Angelo Bassi, Mohammad Bahrami, Tejinder P Singh