Mechanical Quantum Systems

Transcription

1 Mechanical Quantum Systems Matt LaHaye Syracuse University 09 Nov. 2013

2 Outline My field: Mechanical Quantum Systems - What are these systems? - Why are they interesting? What are some of the experimental aspects & challenges of studying these systems? Work we re doing at SU to develop mechanical quantum systems

3 Mechanical Systems in the Quantum Regime Develop and study mechanical quantum devices; devices which under ordinary conditions are perfectly well-described by classical laws of physics Devices like: Microtoroid Resonators Nanomechanical Beams Cleland & Roukes Kippenberg Just a small subset of types of devices being explored. *See M.Poot & H.S. van der Zant, Physics Reports 2012, for a recent and comprehensive review of devices* LIGO Macroscopic Mirrors

4 Mechanical Systems in the Quantum Regime Develop and study mechanical quantum devices; devices which under ordinary conditions are perfectly well-described by classical laws of physics Devices like: Microtoroid Resonators Nanomechanical Beams Cleland & Roukes Kippenberg Vibrational modes normally ring as one would expect for a classical simple harmonic oscillator e.g. well-defined xx and pp as determined by Newton s 2 nd Law; Also continuous energy spectra LIGO Macroscopic Mirrors

5 Mechanical Systems in the Quantum Regime No reason that we know of why the motion of such objects shouldn t exhibit characteristics of quantum S.H.O. (under the right conditions) Roukes Cantilever in a quantum superposition of spatially-separated states From Schwab & Roukes, Phys. Today 2005 EE nn = ħωω(nn ) ωω = kk/mm m k x Discrete Energy Levels Zero-point fluctuations

6 What do We Hope to Accomplish With These Studies? Fundamental studies of quantum mechanics - Shed light on the measurement problem (i.e. quantum-classical boundary ). Think of the Schrodinger Cat Paradox. - Better understanding of fundamental limits of measurement Development of new technologies - For quantum information - For bio-sensing and imaging - For gravitational wave detection - Energy transfer/dissipation at nanoscale e.g. Single-Nuclei Magnetic Imaging e.g. e.g. Long-distance quantum communication Gravitational Wave Detection LIGO interferometer Rabl, Lukin et al. Rugar et al.

7 What are some of the experimental challenges we face in preparing structures in the quantum regime? *For more information/general overview, see: Schwab and Roukes,Physics Today, July 2005.*

8 Thermal Noise EE Energy Spectrum The Environment: (e.g. charge fluctuations ; phonons from substrate, EM radiation, etc) Energy levels only account Roukes for KE and PE due to restoring force PE ħωω 0 Oscillator Embedded in an environment HH = 1 2 kk 0χχ pp 0 2 2mm 0 KE NN = 3 NN = 2 NN = 1 NN = 0 xx EE = ħωω 0 NN Environment is Source of random fluctuations that kick And damp resonator. Nanoresonator as S.H.O. mm kk xx Environment Temp. TT

9 Thermal Noise EE Energy Spectrum ħωω Rule of Thumb: Need kk BBTT ħωω < 1 to see quantum effects The Environment: (e.g. charge fluctuations ; phonons from substrate, EM radiation, etc) Energy levels only account Roukes for KE and PE due to ωωrestoring force Oscillator Embedded in an environment PE ~ MMMMMM 2222 HH = 1 2 kk 0χχ pp 0 2 2mm 0 Need KE TT~ mmmm! In equilibrium: Average Energy EE ~kk BB TT NN = 1 NN = 0 NN = 3 NN = 2 xx Environment is Source of random fluctuations that kick And damp resonator. Fluctuations wash out discrete levels Nanoresonator as S.H.O. mm kk xx Environment Temp. TT

10 Approaching the Ground State of Mechanical Structures Cleland et al., Nature, 2010 ωω/2ππ = 6 GHz TT = 20 mk Teufel et al. Nature 2011 Micro drum head KK BB TT/ħωω =.34 Achieved KK BB TT/ħωω =.1 Painter et al. Nature 2011 Also observed evidence of Energy quantization of the mode Observation of zero-point fluctuations Painter et al. PRL 2012 KK BB TT/ħωω =.85

11 Now that mechanical structures have been cooled near the ground state, how do you prepare and measure quantum states of these structures?

12 Inspiration: Cavity Quantum Electrodynamics (CQED) Measurements of the number state of an EM cavity mode (part of last year s Nobel Physics award) Atom state atom mirror N=1 N=0 State N=0 microwave cavity Electromagnetic Simple Harmonic Oscillator Death of 1 photon Birth of new photon S. Gleyzes et al. Nature 446, (2007) Two internal states (-) and (+)of an atom after passing thru cavity serve as proxies for the 0 and 1 number states of a cavity mode

13 Inspiration: Cavity Quantum Electrodynamics (CQED) Measurements of the number state of an EM cavity mode (part of last year s Nobel Physics award) Atom state N=1 N=0 State N=0 microwave cavity atom or Death of 1 photon Birth of new photon S. Gleyzes et al. Nature 446, (2007) Two internal states (-) and (+) of an atom after passing thru cavity serve as proxies for the 0 and 1 number states of a cavity mode

14 Inspiration from CQED Preparation and measurement of superposition states of an EM cavity mode (part of last year s Nobel Physics award) Prepare the atom in a superposition states before entering the cavity Single atom + The atom and cavity become Entangled in a Schrodinger Cat state Refractive index of cavity depends on state of the atom microwave cavity Cavity evolves into superposition Of states oscillating at different frequencies Raimond et al. Review of Modern Physics, Vol. 73, 565 (2001)

15 Is there some analogous device in solid-state physics that we could use for quantum measurement and manipulation of a nanoresonator?

16 Qubit-Coupled Nanoresonator Analogous to an Atom & Cavity First realized by A. Armour, M. Blencowe & K. Schwab: PRL 88 (2002) & Physica B 316 (2002). Qubit-Coupled Nanoresonator Superconducting Quantum Bit (Qubit) Analogous to Atom-Coupled Electromagnetic Resonator (Cavity) 2 μμmm Nanoresonator In principle, could use superconducting qubits as tools to explore quantum properties of mechanical resonators (including superposition states!) just as atoms have been used for studying quantum properties of electromagnetic resonators in CQED Dozens of theoretical proposals have been put forth to do this, but we have only begun to develop this tool experimentally

17 First Demonstrations of Qubit-Coupled Nanoresonators Nature, 2009 (2010) Cleland et al. demonstrate qubit-based detection of energy quantization in a NR Nature, 2010 (2009) LaHaye et al. demonstrate qubit exerts state-dependent force on NR Coherent swapping of a quantum of energy between NR and qubit NR Nature, 2013 Qubit Just a handful of results. Need to develop further! (2013) Sillanpaa et al. demonstrate mechanical Stark shift of qubit (a prerequisite for many theory proposals to engineer Various quantum states of mechanics)

18 Qubit-Coupled Nanoresonator Research at SU LaHaye Cryogenics Lab Microwave Equipment Experiments at temp. < 3333 mmmm! Funding: NSF-DMR Career Award: # NSF-DMR Materials World Network Award: # Devices made using nanofabrication equipment at SU & Cornell Nanoscale Fabrication Facility (CNF) Research Team Theory Collaborators: Fred Brito (Sao Carlos Institute of Physics) Amir Caldeira (University of Campinas) Postdoc Francisco Rouxinol Visiting Scientist Seung-Bo Shim Grad Student Hugo Hao

19 Conclusions - Mechanics has become a new quantum technology with many possible applications and potential for addressing fundamental questions in quantum mechanics - Qubit-coupled NR will serve as an important test-bed for mechanical quantum systems. Analogous to what CQED has been for studying quantum properties of light. - At SU, we are further developing qubit-coupled NR and in a position to make important contributions to this field