LLNL researchers are advancing quantum computing by refining the classical computing components used in classical-quantum interfaces.
Present-day quantum computing (QC) is accomplished via a combination of classical and quantum hardware. For example, although QC data is stored on qubits (quantum bits), the systems that operate and read the data rely on classical computing platforms.
This interface needs to provide high-fidelity wideband signals to control and measure quantum devices, but it can introduce noise, heat, and restrictions on the overall size and scale of the device.
To balance these undesirable effects, researchers often restrict device operations, but that comes at a cost. For example, setting an upper bound on gate speed reduces noise but can negatively impact processing time.
To improve the scalability and performance of superconducting quantum computing systems, we are building a new classical-quantum interface based on RF photonics.
Conventional digital-to-analog converters rely on electronic upconversion to tune the amplitude and phase of generated radio frequency tones. Although the tuning is necessary, conventional converters are limited by mixer distortion that can compromise quantum experiments.
In contrast, a photonic digital-to-analog converter (PDAC) optically generates RF tones from a train of laser pulses that use electro-optical sampling. The ultrashort duration of these pulses suppresses RF jitter noise, providing excellent phase stability for the resultant RF signals.
Put another way, by sampling the lowest-noise portion of the electronic modulation, the PDAC is able to greatly improve signal-to-noise and distortion (SINAD). In addition to noise benefits, PDAC technology enables faster gates without sacrificing coherence.
Along with implementing PDAC converters, our project will reduce the heat load imparted by the control lines and the thermal background present control signal by replacing RF cabling with optical fiber.
By refining the classical-quantum interface, our project removes artificially imposed constraints on quantum processing and expands the possibilities of quantum computing.
Radio frequency passband signal generation using photonics | Non-Provisional Patent Application, 2020 A. Gowda, J.C.K. Chan, P.T.S. DeVore, D.S. Perlmutter, J.T. Chou
A comparison of LLNL's innovative PDAC (photonic digital-to-analytic converter) versus multiple commercially available electronic signal generators.
Our new classical-quantum interface based on RF photonics reduces noise and distortion when compared with conventional digital-to-analog converters in the few GHz range relevant for superconducting qubits by filtering electronic digital-to-analog converters through an integrated photonic circuit.