Atomic processors

Since the advent of the first microprocessors in 1971, digital technologies have progressed exponentially [Moore et al. 1998] and their capabilities may, in time, seem limitless. However, when digital technologies are used to process a signal, the analog-to-digital conversion stage is problematic, as the digital signal produced is generally degraded compared to the original analog signal: due to quantization, the conversion introduces noise and harmonics to the input signal. In addition, a trade-off must be found between processing dynamics and speed.

Alternative solutions need to be found. One promising approach is analog signal processing on optical carrier. In this context, rare earth ions in crystalline matrix (REIC), well known as gain materials for lasers, offer remarkable properties when cooled to liquid helium temperature. Combining an inhomogeneous width of several tens of GHz with a spectral resolution generally well below 1 MHz, and capable of storing a spectral profile on the microsecond scale for times that can extend to several days, these materials can be used as programmable optical processors for a wide variety of applications. The figure below gives an idea of how an RF signal might be processed by such a processor. The physical phenomenon involved in these applications is spectral hole burning (SHB).

RF signal processing on optical carrier using a "processor" based on a crystal doped with rare-earth ions. The crystal is first optically programmed, and then used as a filter for the signal to be processed. The latter is converted into the optical domain for processing, and can be reconverted into the radio-frequency domain if required.

Principle of spectral holeburning. When an inhomogeneously broadened material is illuminated by a monochromatic radiation, only the active centers resonant with the light source are excited. This radiative excitation leads to the creation of a 2\Gamma_h-wide hole in the absorption profile. In the linear regime, the depth of this hole, representing the number of excited active centers, is proportional to the energy of the incident radiation. Depending on the inhomogeneously broadened materials used, this phenomenon may be permanent (photochemical mechanism) or transient (population transfer).

At Institut Langevin, work on atomic processors focuses on three main areas.

  • Spectral analysis of radio-frequency signals. This project, which began more than 20 years ago in collaboration with the Thales research center and then with researchers at IRCP, aims to resolve the spectral components of a radio-frequency signal to facilitate its subsequent processing by electronic devices. Over the years, the optimization of light-matter interaction [Linget et al., Phys. Rev. A 2015], [Attal et al., JOSA B 2018], the in-depth study of relaxation mechanisms in doped crystals [Ahlefeldt et al., Phys. Rev. B 2015], and the exploration of crystal composition [Welinski et al., Opt. Mat. 2017], [Ferrier et al., J. Lumin. 2018], [Zhang et al., J. Lumin. 2020] have resulted in a promising industrial demonstrator [Berger et al., J. Lightwave Technol. 2016]. Derived functions have also been proposed, such as a high-performance agile photonic filter [Ulrich et al., J. Lightwave Technol. 2022], or a telecom wavelength spectral analyzer [Louchet-Chauvet et al., Las. Phys. 2020].
  • Time reversal. Time reversal allows focusing electromagnetic or sound waves in a heterogeneous medium without precise knowledge of the medium. In the case of broadband radar waves, digital time reversal is not an option, as it cannot cope with a non-stationary propagation medium, due to the excessive latency involved in calculating the reversed field. A few years ago we proposed an architecture for analog time reversal of RF signals on optical carrier based on spectral holeburning in an erbium ion-doped crystal [Linget et al., Opt. Lett. 2013]. The ANR "ATRAP" (Analog Time-Reversal Processor") project currently underway aims to explore a second time-reversal protocol based on photon echo in a doped crystal, more promising in bandwidth [Louchet-Chauvet et al., IEEE MWP 2018].
  • Optomechanics. Optomechanics is a fast-growing field of fundamental physics, which aims to couple a quantum system with a mechanical system. Crystals doped with rare-earth ions are very good candidates for studying this kind of coupling, as the ions are inserted into the crystalline matrix and their energy levels are sensitive to the mechanical stress in the crystal. We proposed to take advantage of this sensitivity to develop a non-contact vibration sensor, operating at low temperatures [Louchet-Chauvet et al., Rev. Sci. Inst. 2019], [Louchet-Chauvet et al., AVS Quantum Science 2022], ideal for diagnosing vibrations in a cryostat for example. We also explored the reciprocal manifestation of this coupling, namely the appearance of mechanical stress caused by optical excitation [Louchet-Chauvet et al., Phys. Rev. Applied 2023] [Louchet-Chauvet et al., J. Phys. Cond. Mat. 2022]. This effect, which we have called "piezo-orbital back-action", is very fundamental and linked to the shape change of atomic orbitals.

Contact:

Anne LOUCHET-CHAUVET
Tel.: +33 (0)1 80 96 30 42
anne.louchet-chauvet (arobase) espci.fr

Collaborations

  • Sacha Welinski, Perrine Berger, Loïc Morvan, Thales Research&Technology Palaiseau
  • Alban Ferrier, Alexey Tiranov, Philippe Goldner, Institut de Recherche de Chimie Paris
  • Pierre Verlot, LuMIn
  • Thierry Chanelière, Signe Seidelin, Jean-Philippe Poizat, Institut Néel
  • Julien de Rosny, Fabrice Lemoult, Institut Langevin

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