Here, we report the experimental demonstration of a novel multi-mode linear bus interferometer (LBI) coupler in a six qubit superconducting quantum processor. A key feature of this coupler is an engineered multi-path interference which eliminates transverse coupling between qubits over a wide frequency range. This negligible static coupling is achieved without any flux bias tuning, and greatly reduces the impact of qubit frequency collisions. We achieve good simultaneous single qubit gate operation and low ZZ rates (below 600 Hz) across the device without staggering qubit frequencies, even in cases where qubits are as close as 10 MHz. Multi-qubit interactions are still possible through the coupler using microwave-driven resonator induced phase gates, which we utilize to demonstrate simultaneous two qubit gates with fidelities as high as 99.4

The cryogenic hardware required to build a superconducting qubit based quantum computer demands a variety of microwave components. These elements include microwave couplers, filters, amplifiers, and circulators/isolators. Traditionally implemented as discrete components, integration of this peripheral hardware, in an effort to reduce overall footprint, thermal load, and added noise, is a key challenge to scaling modern quantum processors with qubit counts climbing over the 100+ mark. Ferrite--based microwave isolators, generally employed in the readout chain to decouple qubits and resonators from readout electronics, persist as one of the volumetrically largest devices still utilized as discrete components. Here we present an alternative two--port isolating integrated circuit derived from the DC Superconducting Quantum Interference Device (DC-SQUID). Non-reciprocal transmission is achieved using the three-wave microwave mixing properties of a flux-modulated DC--SQUID. We show that when multiple DC-SQUIDs are embedded in a multi--pole admittance inverting filter structure, the three-wave mixing derived from the flux pumping of the DC-SQUIDs can provide directional microwave power flow. For a three--pole filter device, we experimentally demonstrate a directionality greater than 15 dB over a 600 MHz bandwidth.

The addition of tunable couplers to superconducting quantum architectures offers significant advantages for scaling compared to fixed coupling approaches. In principle, tunable couplers allow for exact cancellation of qubit-qubit coupling through the interference of two parallel coupling pathways between qubits. However, stray microwave couplings can introduce additional pathways which complicate the interference effect. Here we investigate the primary spectator induced errors of the bus below qubit (BBQ) architecture in a six qubit device. We identify the key design parameters which inhibit ideal cancellation and demonstrate that dynamic cancellation pulses can further mitigate spectator errors.

Implementation of high-fidelity 2-qubit operations is a key ingredient for scalable quantum error correction. In superconducting qubit architectures, tunable buses have been explored as a means to higher-fidelity gates. However, these buses introduce new pathways for leakage. Here we present a modified tunable bus architecture appropriate for fixed-frequency qubits in which the adiabaticity restrictions on gate speed are reduced. We characterize this coupler on a range of 2-qubit devices, achieving a maximum gate fidelity of 99.85%. We further show the calibration is stable over one day.

Fixed-frequency qubits can suffer from always-on interactions that inhibit independent control. Here, we address this issue by experimentally demonstrating a superconducting architecture using qubits that comprise of two capacitively-shunted Josephson junctions connected in series. Historically known as tunable coupling qubits (TCQs), such two-junction qubits support two modes with distinct frequencies and spatial symmetries. By selectively coupling only one type of mode and using the other as our computational basis, we greatly suppress crosstalk between the data modes while permitting all-microwave two-qubit gates.

Droplet microfluidics possesses unique properties such as the ability to carry out multiple independent reactions without dispersion of samples in microchannels. We seek to extend the use of droplet microfluidics to a new range of applications by enabling its integration into workflows based on traditional technologies, such as microtiter plates. Our strategy consists in developing a novel method to manipulate, pool and deliver a precise number of microfluidic droplets. To this aim, we present a basic module that combines droplet trapping with an on-chip valve. We quantitatively analyzed the trapping efficiency of the basic module in order to optimize its design. We also demonstrate the integration of the basic module into a multiplex device that can deliver 8 droplets at every cycle. This device will have a great impact in low throughput droplet applications that necessitate interfacing with macroscale technologies. The micro- to macro- interface is particularly critical in microfluidic applications that aim at sample preparation and has not been rigorously addressed in this context.