Session M30: I/O, Packaging, and 3D Integration for Superconducting and Semiconductor Qubits II

Live

A major challenge towards large-scale quantum computation is the interconnect complexity. In current solid-state qubit implementations, a major bottleneck appears between the quantum chip in a dilution refrigerator and the room temperature electronics. Advanced lithography supports the fabrication of both CMOS control electronics and qubits in silicon. When the electronics are designed to operate at cryogenic temperatures, it can ultimately be integrated with the qubits on the same die or package, overcoming the wiring bottleneck. Here we report a cryogenic CMOS control chip operating at 3 K, which outputs tailored microwave bursts to drive silicon quantum bits cooled to 20 mK. We first benchmark the control chip and find electrical performance consistent with 99.99% fidelity qubit operations, assuming ideal qubits. Next, we use it to coherently control actual silicon spin qubits and find that the cryogenic control chip achieves the same fidelity as commercial instruments. Furthermore, we highlight the extensive capabilities of the control chip by programming a number of benchmarking protocols as well as the Deutsch-Josza algorithm on a two-qubit quantum processor.   

Live

Superconducting electronics often require high-density microwave interconnects capable of transporting signals between temperature stages with minimal loss, cross talk, and heat conduction. We report the design and fabrication of superconducting 53 wt% Nb-47 wt% Ti (Nb47Ti) FLexible coAXial ribbon cables (FLAX). The ten traces each consist of a 0.076 mm Ø NbTi inner conductor insulated with PFA (Ø 0.28 mm) and sheathed in a shared 0.025 mm thick Nb47Ti outer conductor. The cable is terminated with G3PO coaxial push-on connectors via stainless steel capillary tubing (Ø 1.6 mm, 0.13 mm thick) soldered to a coplanar wave guide transition board. The 30 cm long cable has 1 dB of loss at 8 GHz with -60 dB nearest-neighbor forward cross talk. The loss is 0.5 dB more than commercially available superconducting coax likely due to impedance mismatches caused by manufacturing imperfections in the cable. The reported cross talk is 30 dB lower than previously developed laminated NbTi-onKapton microstrip cables. We estimate the heat load from 1 K to 90 mK to be 20 nW per trace, approximately half the computed load from the smallest commercially available superconducting coax from CryoCoax.   

Not Participating

Scaling quantum control and readout connectivity is at the core of the development of the quantum computer. Similar scaling issues arise in earlier steps, for example when investigating production yield and response uniformity of qubits for a given nanotechnology. At this stage, automated and scalable testing solutions are highly desirable to streamline the process, where otherwise manual testing is time consuming and prone to errors. Research centers will strongly benefit from a common and scalable test bench environment, including the interconnection technology with several dozens of signal channels carrying bias, base-band control signals and RF control signals.

As part of the development of a common test environment, the Institut Quantique in Sherbrooke is investigating and characterizing customized multichannel cable solutions from Delft Circuits. To be installed in the Quantum Fablab environment, the multichannel cables under study aim to support high bias voltage (±10V), base-band signaling, RF signaling and embedded IR filtering to minimize noise at the low temperature sample. The presentation will provide a comparative study between the current standard coax cable solution and the customized multichannel cables.   

Live

The capability to perform rapid, high-fidelity, quantum non-demolition measurements is a critical requirement of quantum computers. State-of-the-art superconducting quantum computers achieve this requirement by incorporating multiple microwave components in their output chain, such as Purcell filters, cryogenic circulators and isolators, and quantum limited amplifiers. However, applying such a readout scheme on a large scale is challenging, mainly because cryogenic circulators and isolators rely on magnetic materials and strong magnetic fields, which limit their miniaturization, proximity to the quantum processor, and their direct integration with other components. To solve this problem, we develop nonreciprocal Josephson devices [1] that could replace magnetic circulators and isolators and form in combination with other on-chip components, scalable motherboards for qubit readout [2].

[1] B. Abdo et al., Nat. Commun. 2019.
[2] B. Abdo et al., arXiv 2020.   

Live

As superconducting quantum circuits continue to increase in size and complexity, one bottleneck for scaling becomes the large number of microwave signals lines that must connect room temperature electronics to the cryogenic environment of the device. Typical experiments require multiple coaxial cables per qubit, each heavily filtered and attenuated to ensure excess noise will not degrade qubit coherence, gate fidelity or measurement efficiency. An alternative to this brute force method is to use optical fiber and cryogenic high-speed photodetection as an optical-to-microwave converter, capable of generating shot-noise limited microwave signals directly at millikelvin temperatures. Leveraging the low thermal conductivity, low loss and large intrinsic bandwidth of optical fiber would allow for efficient, massively multiplexed delivery of coherent microwave control pulses. In this talk we demonstrate the control and readout of a superconducting qubit using microwave signals transmitted over optical fiber to the ultracryogenic environment (< 20 mK) and show a proof of principle that this novel method can meet the stringent requirements for superconducting quantum information processing [1].
[1] F. Lecocq, et al, ArXiv 2009.01167 (2020)   

Live

The control of a large quantum processor is typically implemented by channeling shaped microwave signals to the qubits operating at many different frequencies. The conventional techniques based on room temperature electronics encounters restrictions such as the latencies and power consumption.

In this work, we present a quantitative study of an on-chip coherent microwave source based on a Josephson junction strongly coupled to a mode of a superconducting resonator, both theoretically and experimentally. We demonstrate that the source can generate microwave signals with narrow linewidth (<1 Hz), low noise (<-120 dBc/Hz at 1 MHz offset frequency), relatively high output (>25 pW), and a dc-to-rf power conversion efficiency of about 15%. We confirm that the expected infidelity bound arising from the phase noise of our source in a typical quantum-logic operation is below 0.1 % up to 10-ms evolution ensuring that the signal quality is sufficient for the control of quantum systems.   

Live

Silicon based Qubits have been proposed as an alternative to Josephson junction structures when it comes to scaling the quantum processor from hundreds to a thousand Qubits. The control electronics in such system needs to generate a unique RF control and DC bias per Qubit without exceeding the thermal budget of the cryocooler. This paper describes a monolithic integration of the semiconductor quantum core and its associated classic control circuitry manufactured in the 22FDX fully depleted silicon-on-insulator (FD-SOI) technology from GlobalFoundries. The quantum control signal is synthesized from a single RF reference clock that drives the pulse generator for timing control and the 8bit capacitive DAC for amplitude control. The on-chip cryogenic memory stores unique patterns to generate various quantum gate behaviors. The readout circuits use a sampled architecture designed to reduce the common-mode and flicker noise in the front-end. In addition, a fully integrated bias generation system using a single input reference is proposed for a moderately complex 2D quantum structure. The combined area of the entire control circuitry is 0.042mm² while the total power consumption with a reference clock 2.5GHz is 10.7mW at 3.5K.   

Live

As superconducting quantum processors continue to scale up in size, it becomes increasingly challenging to route the required number of control lines through a dilution refrigerator to the qubit chip. In this presentation, we will discuss our efforts to develop high-density fridge wiring for use in next-generation quantum annealers. Our wiring solution is based on flexible multi-channel cables with a stripline geometry, designed to achieve low crosstalk and moderate bandwidth. We will describe the electrical performance of these cables, as well as other design considerations such as thermal management.   

Live

As superconducting quantum processors continue to scale up in size, it becomes increasingly challenging to route the required number of control lines through a dilution refrigerator to the qubit chip. In this presentation, we will discuss our efforts to develop high-density packaging for use in next-generation quantum annealers. Our packaging solutions integrate with our low crosstalk flexible multi-channel cables, and are designed to maintain isolation and moderate bandwidth. We will describe the design and electrical performance of the packages.   

Live

The leakage of microwave photons in the coaxial wiring to a superconducting quantum circuit at frequencies above the superconducting gap of Aluminium (~ 82 GHz) can lead to a reduction in coherence due to quasiparticle generation. The work reports compact cryogenic microwave filters to attenuate higher frequency radiation before reaching superconducting circuits operating in the low GHz range at millikelvin temperatures. The cut-off frequencies between 1 to 10 GHz and the roll-off are set by the filter length, and the absorptive material used in the filter. These parameters are distinct for CR-110 and Esorb-230 tested in the work. The experimental characteristics of the filters are done at room and cryogenic temperatures and up to frequencies of 70 GHz. The calculated coaxial cable attenuation up to 600 GHz including TE and TM modes shows a significant noise photon occupation number at the frequencies above the Aluminium superconducting energy gap. The transmission of Esorb-230 filter material probed at 67 to 110 GHz shows strong attenuation relative to PTFE. The same material can also be used for the outer radiation shielding of the superconducting circuits.   

Live

Deadzone-less, large area camera systems can be assembled by connecting wafer scale sensors to an array of almost reticule size, 4-side tileable, edgeless readout integrated circuits (ROIC). The design of truly edgeless ROICs, with active area extending to their edges, has been made possible with the advent of 3D integration technologies with high-density interconnects, which enable new routing and I/O paradigms. Despite their obvious potential, the realization and widespread development of truly edgeless ROICs to create gapless dectors has faced several obstacles including manufacturing processes related to 3D integration, identification of known good dies and edgeless design methodologies. The advancements required in "thru via" approaches and wafer bonding and its impact on developing integrated electronics required for Quantum and AI will be discussed.   

Live

Conventional coaxial connectivity solutions for quantum computing have limited scaling potential towards and beyond the kQbit era due to cost, connection-density, form-factor and heat-load. In this work, we present a monolithic, multilayer, flexible circuit, which directly connects room temperature electronics to a milliKelvin interface of a quantum device. Specifically, we show the feasibility of scaling towards the kQubit era and beyond by integrating microwave filtering components inside of the flexible substrate. We also present a combination of planar low-pass and infra-red filters that maintains a noise-floor limited stop-band up to 50GHz, suitable for conditioning thermal noise in the millikelvin range. Finally, we address the thermalization of an integrated attenuator, which prevents unwanted localized thermal noise sources present in conventional attenuator solutions.