One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements that expose the technology's lack of high-density, high-speed and power-efficient memory. Here we demonstrate an array of cryogenic memory cells consisting of a non-volatile three-terminal magnetic tunnel junction element driven by the spin Hall effect, combined with a superconducting heater-cryotron bit-select element. The write energy of these memory elements is roughly 8 pJ with a bit-select element, designed to achieve a minimum overhead power consumption of about 30%. Individual magnetic memory cells measured at 4 K show reliable switching with write error rates below 10 -6 , and a 4x4 array can be fully addressed with bit select error rates of 10 -6 . This demonstration is a first step towards a full cryogenic memory architecture targeting energy and performance specifications appropriate for applications in superconducting high performance and quantum computing control systems, which require significant memory resources operating at 4 K.An issue with the SHE-MTJ, however, is that its characteristic impedance and switching currents are too large to be directly compatible with our separately fabricated SFQ control circuits. For example, a 300 nm wide, 5 nm thick spin Hall channel requires a switching current of roughly 1 mA into a 0.5 kΩ load, which is incompatible with typical SFQ circuit output impedance of a few Ohms.

The functionality of a nanowire integrated into a superconducting transmission line acting as a single pole single throw switch is demonstrated. The switch has an instantaneous bandwidth from 2 to 8 GHz with more than 10 dB of isolation between the open and closed states. The switch consumes no power in the closed state and ≈ 15 nW in the open state. The rise and fall response time between open and closed states is approximately 370 ps. PACS numbers: #Quantum computing architectures employing as many as 72 qubits have recently been demonstrated. In order to scale such architectures further, miniaturized circulators, isolators, and switching networks that have low power consumption while operating at cryogenic temperatures will be necessary 1 . Several groups have demonstrated microwave switches and phase shifters based on Josephson junctions 2-6 , and novel semiconductor devices 1,7 . A cryogenic switch operating at DC, based on a cryotron has also been reported 8 . In this letter, we demonstrate a single pole single throw (SPST) switch fabricated from a nanowire integrated into a superconducting transmission line as an alternative low power, cryogenic microwave switch. Such nanowires are commonly used in the fabrication of superconducting single photon detectors 9-12 , and a three terminal variant of the device has been shown to operate as a transistor for digital logic applications 13 . We present two variants of the switch, one with a single nanowire and a second with two nanowires operated in tandem to provide improved isolation between the open and closed states of the switch. The single nanowire device is a small, w = 80 nm wide nanowire integrated into a superconducting transmission line with two on-chip inductors fabricated in a single metal layer. Surface mount capacitors are soldered off chip onto the transmission line feeding the device, creating a bias tee. Modulation of the switch is achieved by applying a low frequency signal to the inductive ports of the bias tee of sufficient power to exceed the critical current of the nanowire. The switch is in the closed state when the nanowire is superconducting and forms a lossless transmission line. Similarly the switch is open when the nanowire has been driven into the normal state. The switches are fabricated on a single layer of d = 8 nm thick NbN with a sheet resistance of ≈ 356 Ω/square. A wire only 3 squares long fabricated from this material will produce an impedance of ≈ 1 kΩ in the resistive state, enough to obtain more than 20 dB of RF isolation. In the tandem nanowire design a second nanowire increases isolation by shorting one RF port to ground while the first nanowire is simultaneously in the normal state. a) andrew.wagner@raytheon.com V S1 S2 2 µm (a) S1 S2 V 1 V 2 2 µm (b) FIG. 1. SEM micrograph images and circuit diagrams of the single nanowire switch (a) and tandem nanowire switch (b).The single nanowire switch is actuated by a voltage signal V that drives current through a resistor connected to the inductors of the bias tee. The tandem nanow...

To mimic in vivo vibration of vocal fold cells, we studied the controllability and range of frequency, acceleration, duration, and shear stress in a new bioreactor attachment. The custom multiwell disc appliance fits into a commercially built rheometer, together termed a torsional rheometer bioreactor (TRB). Previous attachments to the TRB were capable of 50-100 Hz vibrations at relatively high strains but were limited to single-sample experiments. The TRB-multiwell disc system accommodates 20 samples in partially fluid-filled wells in an aseptic environment delivering three different acceleration conditions to different samples simultaneously. Frequency and amplitude used to calculate acceleration along with duration and shear stress were controllable and quantifiable using a combination of built-in rheometer sensors, manufacturer software, and smooth particle hydrodynamics (SPH) simulations. Computed shear stresses at the well bottom using SPH in two and three dimensions were verified with analytical approximations. Results demonstrate capabilities of the TRB-multiwell disc system that, when combined with computational modeling, provide quantifiable vibration parameters covering frequencies 0.01-250 Hz, accelerations of 0.02-300 m/s 2 , and shear stresses of 0.01-1.4 Pa. It is

Control electronics for superconducting quantum processors have strict requirements for accurate command of the sensitive quantum states of their qubits. Hinging on the purity of ultra-phase-stable oscillators to upconvert very-low-noise baseband pulses, conventional control systems can become prohibitively complex and expensive when scaling to larger quantum devices, especially as high sampling rates become desirable for fine-grained pulse shaping. Few-gigahertz radio-frequency (RF) digital-to-analog converters (DACs) present a more economical avenue for high-fidelity control while simultaneously providing greater command over the spectrum of the synthesized signal. Modern RF DACs with extra-wide bandwidths are able to directly synthesize tones above their sampling rates, thereby keeping the system clock rate at a level compatible with modern digital logic systems while still being able to generate high-frequency pulses with arbitrary profiles. We have incorporated custom superconducting qubit control logic into off-the-shelf hardware capable of low-noise pulse synthesis up to 7.5 GHz using an RF DAC clocked at 5 GHz. Our approach enables highly linear and stable microwave synthesis over a wide bandwidth, giving rise to high-resolution control and a reduced number of required signal sources per qubit. We characterize the performance of the hardware using a five-transmon superconducting device and demonstrate consistently reduced two-qubit gate error (as low as 1.8%), which we show results from superior control chain linearity compared to traditional configurations. The exceptional flexibility and stability further establish a foundation for scalable quantum control beyond intermediate-scale devices. INDEX TERMSClassical control and readout electronics, microwave techniques, quantum computing, superconducting qubits. Engineering uantum Transactions on IEEE Kalfus et al.: HIGH-FIDELITY CONTROL OF SUPERCONDUCTING QUBITS