Jean-Louis Le Gouët

Demonstration of a radio-frequency spectrum analyzer based on spectral hole burning.

Spectral hole-burning (SHB) technology is considered for >10‐GHz instantaneous bandwidth signal-processing applications. In this context we report on what is believed to be the first demonstration of a SHB microwave spectrometer. A set of gratings engraved in a SHB crystal is used to filter one sideband of the optically carried microwave signal. The setup is confined to narrow-bandwidth operation, over a 35-MHz-wide interval. The first findings confirm the validity of the architecture in terms of spectral resolution, angular channel separation, and simultaneous detection of multiple spectral lines.

Why the two-pulse photon echo is not a good quantum memory protocol

We consider in this paper a two-pulse photon echo sequence in the prospect of quantum light storage. We analyze the conditions where quantum storage could be realistically performed. We simply and analytically calculate the efficiency in that limit, and clarify the role of the exactly {pi}-rephasing pulse in the sequence. Our physical interpretation of the process is well supported by its experimental implementation in a Tm{sup 3+}:yttrium aluminum garnet crystal thanks to an accurate control of the rephasing pulse area. We finally address independently the fundamental limitations of the quantum fidelity. Our work allows us to point out on one side the real drawbacks of this scheme for quantum storage and on the other side its specificities which can be a source of inspiration to conceive more promising procedures with rare-earth ion doped crystals.

Phase locking of a frequency agile laser

The authors report on the development and phase locking of a frequency agile laser. The use of a simple unbalanced Mach-Zehnder interferometer together with a wideband phase-locked loop permits to control very fast frequency chirps (up to 3GHz in 5μs) with an excellent precision (frequency error less than 100kHz). The servoloop could be applied to many tunable lasers.

Demonstration of a radio-frequency spectrum analyser based on spectral hole burning

We demonstrate application of spectral hole burning to the spectral analysis of broad-band rf signals. In quite the same way as an acousto-optic spectrometer, the device operates on an optically carried rf signal and achieves angular separation of the signal spectral components. An instantaneous bandwidth of 2.5 GHz has been achieved, with a power dynamic range of 35 dB, limited by the detector. Extension to greater than 10 GHz instantaneous bandwidth with greater than 1000 channels is consistent with the active material capabilities.

RF spectrum analysis in spectral hole burning media

We demonstrate an RF spectrum analyzer based on spectral-hole burning (SHB) that operates with unity probability of intercept and resolution under 100 kHz. An SHB crystal, which consists of rare-earth ions doped into a crystal host, records the power spectrum of an RF signal modulated onto an optical carrier as a series of spectral holes that persist for about 10 ms. While the crystals homogeneous and inhomogeneous linewidths place the fundamental limits on resolution and bandwidth, respectively, the practical limits depend on the lasers used to interrogate the record stored in the crystals absorption profile. Up to now, SHB spectrum analyzers have used chirped beams from externally modulated, stabilized lasers, which have linewidths of under 10 kHz but cannot chirp over much more than octave bandwidths, or directly modulated diode lasers, which can chirp over more than 20GHz but have linewidths of about 1 MHz. Switching to chirped fiber lasers, which have natural linewidths of under 2 kHz and chirping linewidths on the order of 10 kHz, produces a measurement with fine resolution without any laser stabilization. In addition, by chirping the fiber laser with a sufficiently fast piezo, the resulting chirp could extend over tens of gigahertz in under 10 ms, yielding both fine resolution and broad bandwidth without extraordinary stabilization schemes.

Large efficiency at telecom wavelength for optical quantum memories.

The use of erbium doped materials has revolutionized fiber-optic communications. The erbium-doped fiber amplifier is a key enabling technology already emblematic of our century. Its transposition to the quantum communication world is an active subject of research showing interesting possibilities for long distance quantum cryptography [1, 2]. The direct use of erbium-doped fiber as an optical quantum memory is extremely appealing. Nevertheless the coherence time necessary to preserve the quantumness falls in the microsecond range even at subKelvin temperature [3]. Instead of amorphous materials [4], crystalline samples namely Er:Y2SiO5 have shown remarkably long optical coherence time for solids [5]. These engaging properties are unfortunately counterbalanced by poor optical pumping dynamics. Spectral hole-burning (SHB) required by most of the quantum storage protocols is particularly challenging in erbium doped solids [6]. This intrinsic limitation is both due to the short lifetime of the population possibly shelved in the Zeeman sublevels (< 100 ms [6]) and to the long excited state population lifetime (∼ 10 ms). The ratio between the two timescales is not sufficient to obtain a good state preparation for optical thick samples. This simple experimental observation drastically bridles the implementation of quantum memories [7]. As an example, using the protocol named CRIB for controlled reversible inhomogeneous broadening derived from the photon-echo technique, Lauritzen obtained an efficiency of 0.25% in Er:Y2SiO5 [8] but Hedges reached 69% in Pr:Y2SiO5 [9] essentially explained by different optical pumping dynamics. We recently proposed a protocol called Revival Of Si-We implement the ROSE protocol in an erbium-doped solid, compatible with the telecom range. The ROSE scheme is an adaptation of the standard two-pulse photon echo to make it suitable for a quantum memory. We observe a retrieval efficiency of 40% for a weak laser pulse in the forward direction by using specific orientations of the light polarizations, magnetic field, and crystal axes.

Amplitude and phase measurements of femtosecond pulses shaped by use of spectral hole burning in free-base naphthalocyanine-doped films

We performed pulse-shaping and time-reversal experiments using spectral holography based on persistent spectral hole burning in free-base naphthalocyanine-doped films. We demonstrate that we can control the pulses diffracted from the hologram by shaping and then by characterizing these pulses in both amplitude and phase. A dephasing time of 29 ps (i.e., a homogeneous linewidth of 69 GHz) was measured from a photon-echo experiment in the chemically accumulated regime.

10GHz Bandwidth rf spectral analyzer with megahertz resolution based on spectral-spatial holography in Tm 3+ :YAG: experimental and theoretical study

Different architectures of rf spectral analyzers based on the spectral photography scheme in spectral-hole-burning materials are theoretically and experimentally investigated. The microscopic atomic response for the recording and reading of the rf spectra and taking into account the spatial extension of the beams is calculated for different analyzer configurations. The spectral resolution and the signal-to-noise ratio of the analyzer are derived. These predictions are experimentally tested using spectral-hole burning in Tm3+:YAG for a couple of configurations and sizes of the beams. In each case, the resolution, linear dynamic range, and bandwidth of the spectrum analyzer are determined.

Optical memory bandwidth and multiplexing capacity in the erbium telecommunication window

We study the bandwidth and multiplexing capacity of an erbium-doped optical memory for quantum storage purposes. We concentrate on the protocol ROSE (Revival of a Silenced Echo) because it has the largest potential multiplexing capacity. Our analysis is applicable to other protocols that involve strong optical excitation. We show that the memory performance is limited by instantaneous spectral diffusion and we describe how this effect can be minimised to achieve optimal performance.

Securing coherence rephasing with a pair of adiabatic rapid passages

Coherence rephasing is an essential step in quantum storage protocols that use echo-based strategies. We present a thorough analysis on how two adiabatic rapid passages (ARPs) are able to rephase atomic coherences in an inhomogeneously broadened ensemble. We consider both optical and spin coherences, rephased by optical or radio-frequency (rf) ARPs, respectively. We show how a rephasing sequence consisting of two ARPs in a double-echo scheme is equivalent to the identity operator (any state can be recovered), as long as certain conditions are fulfilled. Our mathematical treatment of the ARPs leads to a very simple geometrical interpretation within the Bloch sphere that permits a visual comprehension of the rephasing process. We also identify the conditions that ensure the rephasing, finding that the phase of the optical or rf ARP fields plays a key role in the ability of the sequence to preserve the phase of the superposition state. This settles a difference between optical and rf ARPs, since field phase control is not readily guaranteed in the former case. We also provide a quantitative comparison between π-pulse and ARP rephasing efficiencies, showing the superiority of the latter. We experimentally verify the conclusions of our analysis through rf ARP rephasing sequences performed on the rare-earth ion-doped crystal Tm3+:YAG, of interest in quantum memories.