Brillouin-Mandelstam scattering offers several favourable properties to control sound with light at a quantum mechanical level. In particular, the high acoustic frequencies, acoustic mode selectivity, and low optical absorption provide a promising route towards this goal whilst also overcoming several current hindrances within optomechanics. Utilizing these properties, some of our main results in this direction include: the first observation of Brillouin optomechanical strong coupling, studying the second-order coherence across the Brillouin lasing threshold, and, we’ve performed heralded single-phonon addition and subtraction to a thermal state of the acoustic field observing the resulting non-Gaussianity with a precision that advanced the forefront of opticsbased mechanical state tomography. More recently, we’ve demonstrated that laser cooling may be enhanced via zero-photon detection, and we’ve characterized the Brillouin scattering response in optical fibre at millikelvin temperatures. This talk will cover these results, what they enable, and the broader direction of our lab including the prospects of this platform for quantum science and technology.
Brillouin-Mandelstam scattering offers several favourable properties to control sound with light at a quantum mechanical level. In particular, the high acoustic frequencies, acoustic mode selectivity, and low optical absorption provide a promising route towards this goal whilst also overcoming several current hindrances within optomechanics. Utilizing these properties, some of our main results in this direction include: the first observation of Brillouin optomechanical strong coupling, studying the second-order coherence across the Brillouin lasing threshold, and, we’ve performed heralded single-phonon addition and subtraction to a thermal state of the acoustic field observing the resulting non-Gaussianity with a precision that advanced the forefront of opticsbased mechanical state tomography. More recently, we’ve demonstrated that laser cooling may be enhanced via zero-photon detection, and we’ve characterized the Brillouin scattering response in optical fibre at millikelvin temperatures. This talk will cover these results, what they enable, and the broader direction of our lab including the prospects of this platform for quantum science and technology.
Brillouin–Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave-mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a “flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the “flickering,” are a result of the full nonlinear three-wave-mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.
Recognized as a potential resource for quantum technologies and a possible test bed for fundamental physics, the control and preparation of nonclassical states of mechanical oscillators have been explored extensively. Within optomechanics, quantum state synthesis can be realized by entangling photonic and phononic degrees of freedom followed by optical detection. Single-photon detection enables one of the most powerful forms of such heralded quantum state preparation, permitting the creation of single-phonon states when applied to conventional cavity optomechanical systems. As the complexity of optomechanical systems increases, single-photon detection may provide heralded access to a larger class of exotic quantum states. Here, we examine the quantum dynamics of optomechanical systems that permit forward Brillouin scattering, where a single-phonon mode mediates transitions between a collection of equally spaced optical resonances. Solving both the Schrodinger equation and the Lindblad master equation for this system, we find that initial states comprised of single photons or weak laser pulses evolve into complex quantum states where the frequency of single-photon states and the phonon occupation number are entangled. Physically, these interactions permit a single photon to scatter to lower frequencies, where phonon excitation occurs for each scattering event. Combining this result with frequency filtering, we show how single-photon detection can herald selected multiphonon Fock states, even in the presence of optical losses. We also present an approach for quantum tomography of the heralded phonon states, which in the form of a state swap from the phononic to photonic domain enables on-demand generation of multiphoton Fock states.
Optical and acoustic waves can interact over the nonlinear effect of stimulated Brillouin scattering (SBS), which is a coherent process. By using traveling acoustic waves, we recently showed proof-of-principle experiments of Brillouin-based light storage. The particularity of Brillouin-based light storage is the strict phase-matching condition. This allows for different features: simultaneous storage at multiple wavelengths, cascaded storage at different spatial positions, and nonreciprocal storage with a GHz bandwidth. However, the delay time of this technique has so far been limited to the acoustic lifetime of about 10 ns. In this talk, I will discuss our recent results on coherent photon-phonon interaction. One focus will be on a proof-of-principle experiments on how to reinforce acoustic phonons. This enables us to overcome the obstacle of the limited acoustic lifetime by optically reinforcing the acoustic wave.
Stimulated Brillouin scattering drives a coherent interaction between optical signals and acoustic phonons and can be used for storing optical information in acoustic waves. An important consideration arises when multiple optical frequencies are simultaneously employed in the Brillouin process: in this case, the acoustic phonons that are addressed by each optical wavelength can be separated by frequencies far smaller than the acoustic phonon linewidth, potentially leading to cross talk between the optical modes. Here we extend the concept of Brillouin-based light storage to multiple wavelength channels. We experimentally and theoretically show that the accumulated phase mismatch over the length of the spatially extended phonons allows each optical wavelength channel to address a distinct phonon mode, ensuring negligible cross talk and preserving the coherence, even if the phonons overlap in frequency. This phase-mismatch for broad-bandwidth pulses has far-reaching implications allowing dense wavelength multiplexing in Brillouin-based light storage, multifrequency Brillouin sensing and lasing, parallel microwave processing, and quantum photon-phonon interactions.
In silica glass fibers, thermally excited acoustic phonons scatter light into the beam propagating in the forward direction. At acoustic frequencies up to several hundreds of megahertz, the wave vectors of the phonons interacting with the light propagate essentially transversally to the fiber axis. This effect is known as Guided Acoustic Wave Brillouin Scattering (GAWBS) and leads to phase and polarization noise in the guided light. For fiber-based quantum optics experiments, this excess noise is a major limitation. In Photonic Crystal Fibers (PCFs), light is guided by a microstructure simultaneously acting as a 2D transversal phononic crystal which modifies the acoustic noise spectrum. We demonstrate a GAWBS-noise reduction in commercially available PCFs. This gives rise to the prospect of fiber-based quantum optic devices exhibiting less excess noise, thus resulting in higher quantum state purity. Further improvement can be achieved by tailoring the photonic microstructure such that a reduction of phonon noise by design is achieved.
Due to its high coherence in transmission over a large distance in the ambient environment, the quantum optical system has been a prevailing platform for long-distance quantum communication, which was recently realized over a continental distance with a low earth orbit satellite and ground stations [102, 70]. However, the pure quantum optical system has so far shown weak interactions between photon and matter, which makes it inefficient in carrying out deterministic quantum gates for quantum repeater based scalable quantum network and quantum computing. On the other hand, superconducting quantum systems operating in the microwave domain with Josephson junction transmon qubits have proven to be capable of efficient deterministic quantum operations on quantum states [86, 87, 66]. Nevertheless, such architecture is prone to errors and decoherence due to cross-talk between microwave elements in a large-scale superconducting quantum circuit. Furthermore, superconducting systems, in general, also have large footprint (100s um) elements (resonators and superconducting quantum bits) [92, 60] that limit the ability to scale up a superconducting quantum system. Moreover, microwave quantum circuits require cooling to around 10 mK, making it unsuitable for communicating quantum information outside a dilution refrigerator (DF). Micro- and nano- acoustic elements have been extensively used in conventional integrated information processing systems due to their compactness and high coherence [97]. Acoustic systems in quantum engineering also have the advantage of being a platform for universal couplings between various quantum systems including spins, optical photons, and superconducting circuits. As it will be discussed in this thesis, elements critical to scalable optical quantum network and superconducting quantum circuit can be constructed relying on the cavity optomechanics and piezoelectric interactions. Optomechanical interaction is concerned with the light pressure coupling of cavity mechanical deformation to a strong optical field. This interaction has allowed the close to mechanical ground state cooling of mechanical resonators using laser and the ultra-sensitive displacement measurement that led to the detection of gravitational waves in the LIGO collaboration [125, 25]. Optomechanical crystals (OMCs) are lithographically patterned devices which contain a periodic structure that host bandgaps for both optical band electromagnetic waves and microwave band acoustic waves. A properly engineered defect in the crystal can confine and localize acoustic and electromagnetic modes of similar wavelengths into a small mode volume [17, 20, 21]. A strong optomechanical coupling, which can be achieved between such strongly confined co-localized optical and acoustic modes, can be used in engineering the quantum state of mechanical motion to realize useful quantum devices such as a high-coherence quantum memory [74] and an optomechanical high efficiency optical isolator for unidirectionally connecting distant optical cavities via an acoustic bus [37]. To strongly couple the mechanical degree of freedom with a superconducting quantum circuit, various methods can be used, ranging from electromechanic coupling (electric coupling to a mechanically compliant capacitor), magnetomechanical coupling (magnetic coupling to a vibrating SQUID loop), and piezoelectric coupling. The recent advent of quantum acoustics [23, 8, 9] was realized with the strong piezoelectric coupling between a superconducting transmon qubit and a high-coherence mechanical resonator. The engineered strong piezoacoustic coupling provides the possibility to carry out deterministic ultra-high fidelity two-qubit quantum gates on non-classical mechanical quantum states [52]. This ability together with the recent demonstration of ultra-long phonon lifetime mechanical resonators show the possibility of integrating the ultra-high quality mechanical resonator as a compact quantum memory element and even a new ultra-compact (10s um) quantum bit architecture for scalable superconducting quantum circuits. Furthermore, the strong piezoelectric coupling that can transduce quantum state in a superconducting circuit into mechanical wave also makes it possible to efficiently transduce a quantum state between a superconducting quantum circuit and a telecommunication band optical channel via a mechanical waveguide connected to an optomechanical crystal cavity.