Engineering of Quantum Dynamics with Local Addressability in Micro-Cavity Arrays

• Applicant: Professor Dr. Michael J. Hartmann
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2008 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 60515387

• Final Report Year: 2014

Final Report Abstract

Networks of interacting photons Photons are the ideal carrier for transmitting information over long distances as they are largely immune to environmental perturbations and propagate with very low loss and long-lived coherence in a wide range of media. Yet, the use of photons in information processing still suffers from difficulties to realize controlled, strong interactions between individual photons. To make photons a more versatile information carrier, it is therefore of utmost importance to conceive means of making photonic signals interact with each other at various nodes of a network. Besides technological applications these new physical systems with distributed strong photon-photon interactions give rise to new quantum many-body physics of strongly correlated photons. My group and I have devised new approaches to such quantum many-body systems of interacting photons which significantly enhance the feasibility of realizing these in experiments. For optical photons we have shown that dissipative interactions in tapered optical fibers can be employed instead of elastic scattering. This increases the strength of interactions by an order of magnitude whereas using a fiber avoids the need of building mutually resonant optical cavities. We have furthermore devised approaches for generating quantum many-body systems of interacting microwave photons in superconducting circuits, which are ideally amenable for experimental implementations as the show pronounced strong coupling regimes and can due to their size be built resonantly with each other. We have introduced methods for efficient descriptions of these systems, predicted new phases for interacting photons in such arrays of coupled circuit cavities, and introduced a scheme for a single photon transistor. Nonclassical states of nanomechanical oscillators A new regime of quantum physics is currently explored in optomechanics, where small mechanical oscillators couple to light. A recent breakthrough in this field was achieved when mechanical oscillators have for the first time been cooled to their ground states. Yet, such harmonic oscillators have ground states that are Gaussian and do not show any distinguished quantum features. Pure quantum correlations in the form of entanglement can however exist between two mechanical oscillators in a common Gaussian state and I have developed a scheme that drives two nanomechanical oscillators into a long lived stationary state that exhibits entanglement between both. To explore genuine quantum physics of single mechanical oscillators, I have developed a new regime of optomechanics together with my group. Mechanical oscillators that are clamped at both ends always feature a nonlinear contribution to their restoring force, which usually is negligibly small for small deflection amplitudes. Applying electrostatic forces to the mechanical oscillator, we showed that this nonlinearity can be enhanced to such an extent that individual phonons can be manipulated with optomechanical forces. As one application, this approach allows to generate stationary phonon Fock states, which are genuine quantum states with negative values in their Wigner function. As a second application we have shown that a universal set of quantum gates can be implemented for quantum information that is stored in the mechanical motion of such oscillators. This result was subject of a press release by Technische Universität München (http://www.ph.tum.de/latest/news/138/) and had been extensively covered in the scientific media (see e.g. http://science.orf.at/stories/1714989/, http://www.pro-physik.de/details/news/4518601/Quantencomputer_aus_Kohlenstoff-Nanoroehrchen. html, or http://www.heise.de/ct/meldung/Quantencomputer-mit-Saiteneffekt-1828096.html).

Publications

• Synchronized switching in a Josephson junction crystal Phys. Rev. Lett. 112, 223603 (2014)
  M. Leib and M. J. Hartmann
  
• Bose-Hubbard dynamics of polaritons in a chain of circuit quantum electrodynamic cavities New J. Phys. 12, 093031 (2010)
  M. Leib and M.J. Hartmann
  
• Dissipation induced Tonks-Girardeau gas of polaritons. Phys. Rev. A 81, 021806(R) (2010)
  M. Kiffner and M.J. Hartmann
  
• Polariton crystallization in driven arrays of lossy nonlinear resonators Phys. Rev. Lett. 104, 113601 (2010)
  M. J. Hartmann
  
• Photon Blockade in the Ultrastrong Coupling Regime Phys. Rev. Lett. 109, 193602 (2012)
  A. Ridolfo, M. Leib, S. Savasta and M. J. Hartmann
  
• Steady-state negative Wigner functions of nonlinear nanomechanical oscillators. New J. Phys. 14, 023042 (2012)
  S. Rips, M. Kiffner, I. Wilson-Rae and M.J. Hartmann
  
• Photon solid phases in driven arrays of non-linearly coupled cavities Phys. Rev. Lett. 110, 163605 (2013)
  J. Jin, D. Rossini, R. Fazio, M. Leib, and M. J. Hartmann
  
• Quantum Information Processing with Nanomechanical Qubits Phys. Rev. Lett. 110, 120503 (2013)
  S. Rips, and M. J. Hartmann
  
• Single Photon Transistor in Circuit Quantum Electrodynamics Phys. Rev. Lett. 111, 063601 (2013)
  L. Neumeier, M. Leib, and M. J. Hartmann
  
• Self-Consistent Projection Operator Theory for Quantum Many-Body Systems Phys. Rev. B 89, 245108 (2014)
  P. Degenfeld-Schonburg and M. J. Hartmann