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Quantum technologies

Dieter Meschede's research group
Home Group members Tobias Macha
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Group members
Dipl.-Phys. Tobias Macha
Contact
Position: PhD student
Field of research: Fibre cavity QED
Address:
Institut für Angewandte Physik
Wegelerstr. 8
D-53115 Bonn
Germany
Office room: 113
Laboratory room: 219
E-mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it.
Office: +49 228 73-3482
Laboratory: +49 228 73-3485
Fax: +49 228 73-3474
 

Publications

  • J. Gallego, W. Alt, T. Macha, M. Martinez-Dorantes, D. Pandey and D. Meschede
    Strong Purcell effect on a neutral atom trapped in an open fiber cavity, Phys. Rev. Lett. 121, 17360 (2018)arXivBibTeXPDF
    ABSTRACT »

    We observe a sixfold Purcell broadening of the D2 line of an optically trapped 87Rb atom strongly coupled to a fiber cavity. Under external illumination by a near-resonant laser, up to 90% of the atom's fluorescence is emitted into the resonant cavity mode. The sub-Poissonian statistics of the cavity output and the Purcell enhancement of the atomic decay rate are confirmed by the observation of a strongly narrowed antibunching dip in the photon autocorrelation function. The photon leakage through the higher-transmission mirror of the single-sided resonator is the dominant contribution to the field decay (κ≈2π×50 MHz), thus offering a high-bandwidth, fiber-coupled channel for photonic interfaces such as quantum memories and single-photon sources.

  • M. Zopf, T. Macha, R. Keil, E. Uruñuela, Y. Chen, W. Alt, L. Ratschbacher, F. Ding, D. Meschede and O. G. Schmidt
    Frequency feedback for two-photon interference from separate quantum dots, Phys. Rev. B 98, 161302(R) (2018)arXivBibTeXPDF
    ABSTRACT »

    We employ active feedback to stabilize the frequency of single photons emitted by two separate quantum dots to an atomic standard. The transmission of a rubidium-based Faraday filter serves as the error signal for frequency stabilization. We achieve a residual frequency deviation of <30 MHz, which is less than 1.5% of the quantum dot linewidth. Long-term stability is demonstrated by Hong-Ou-Mandel interference between photons from the two quantum dots. Their internal dephasing limits the expected visibility to V = 40%. We observe Vlock = (41±5)% for frequency-stabilized dots as opposed to Vfree = (31±7)% for free-running emission. Our technique reaches the maximally expected visibility for the given system and therefore facilitates quantum networks with indistinguishable photons from distributed sources.

  • R. Reimann, W. Alt, T. Kampschulte, T. Macha, L. Ratschbacher, N. Thau, S. Yoon and D. Meschede
    Cavity-Modified Collective Rayleigh Scattering of Two Atoms, Phys. Rev. Lett. 114, 023601 (2015)arXivBibTeXPDF
    ABSTRACT »

    We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case (N=2) is almost equal to the single-emitter case (N=1), which is in contrast to free-space where one would expect an N^2 scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic.

  • R. Reimann, W. Alt, T. Macha, D. Meschede, N. Thau, S. Yoon and L. Ratschbacher
    Carrier-free Raman manipulation of trapped neutral atoms, New J. Phys. 16, 113042 (2014)arXivBibTeXPDF
    ABSTRACT »

    We experimentally realize an enhanced Raman control scheme for neutral atoms that features an intrinsic suppression of the two-photon carrier transition, but retains the sidebands which couple to the external degrees of freedom of the trapped atoms. This is achieved by trapping the atom at the node of a blue detuned standing wave dipole trap, that acts as one field for the two-photon Raman coupling. The improved ratio between cooling and heating processes in this configuration enables a five times lower fundamental temperature limit for resolved sideband cooling. We apply this method to perform Raman cooling to the two-dimensional vibrational ground state and to coherently manipulate the atomic motion. The presented scheme requires minimal additional resources and can be applied to experiments with challenging optical access, as we demonstrate by our implementation for atoms strongly coupled to an optical cavity.


Colloquia