An integrated microwave-to-optics interface for scalable quantum computing.

Microwave-to-optics transduction is emerging as a vital technology for scaling quantum computers and quantum networks. To establish useful entanglement links between qubit processing units, several key conditions must be simultaneously met: the transducer must add less than a single quantum of input-referred noise and operate with high efficiency, as well as large bandwidth and high repetition rate. Here we present a design for an integrated transducer based on a planar superconducting resonator coupled to a silicon photonic cavity through a mechanical oscillator made of lithium niobate on silicon. We experimentally demonstrate its performance with a transduction efficiency of 0.9% with 1 µW of continuous optical power and a spectral bandwidth of 14.8 MHz. With short optical pulses, we measure the added noise that is limited to a few photons, with a repetition rate of up to 100 kHz. Our device directly couples to a 50 Ω transmission line and can be scaled to a large number of transducers on a single chip, laying the foundations for distributed quantum computing.

Ultra-low-noise microwave to optics conversion in gallium phosphide.

Mechanical resonators can act as excellent intermediaries to interface single photons in the microwave and optical domains due to their high quality factors. Nevertheless, the optical pump required to overcome the large energy difference between the frequencies can add significant noise to the transduced signal. Here we exploit the remarkable properties of thin-film gallium phosphide to demonstrate bi-directional on-chip conversion between microwave and optical frequencies, realized by piezoelectric actuation of a Gigahertz-frequency optomechanical resonator. The large optomechanical coupling and the suppression of two-photon absorption in the material allows us to operate the device at optomechanical cooperativities greatly exceeding one. Alternatively, when using a pulsed upconversion pump, we demonstrate that we induce less than one thermal noise phonon. We include a high-impedance on-chip matching resonator to mediate the mechanical load with the 50-Ω source. Our results establish gallium phosphide as a versatile platform for ultra-low-noise conversion of photons between microwave and optical frequencies.

Photosystem I - based biohybrid photoelectrochemical cells.

Photosynthesis is the process by which Nature coordinates a tandem of protein complexes of impressive complexity that function to harness staggering amounts of solar energy on a global scale. Advances in biochemistry and nanotechnology have provided tools to isolate and manipulate the individual components of this process, thus opening a door to a new class of highly functional and vastly abundant biological resources. Here we show how one of these components, Photosystem I (PSI), is incorporated into an electrochemical system to yield a stand-alone biohybrid photoelectrochemical cell that converts light energy into electrical energy. The cells make use of a dense multilayer of PSI complexes assembled on the surface of the cathode to produce a photocatalytic effect that generates photocurrent densities of approximately 2 microA/cm(2) at moderate light intensities. We describe the relationship between the current and voltage production of the cells and the photoinduced interactions of PSI complexes with electrochemical mediators, and show that the performance of the present device is limited by diffusional transport of the electrochemical mediators through the electrolyte. These biohybrid devices display remarkable stability, as they remain active in ambient conditions for at least 280 days. Even at bench-scale production, the materials required to fabricate the cells described in this manuscript cost approximately 10 cents per cm(2) of active electrode area.