Enclosure H - Technical Specifications.pdf

Technical Specifications Dilution Refrigerator for Superconducting Quantum Circuit Measurements

Overview

The Co-design Center for Quantum Advantage (C2QA) at Brookhaven National Laboratory is planning to acquire a dilution refrigerator system for near-quantum-limited characterization of various quantum information circuits (“DRSQ”), including superconducting qubit and high-Q microwave resonators. The DRSQ should be a cryogen-free (“dry”) system and optimized for high-fidelity DC/RF measurements of superconducting circuits. It must enable integration of multiple RF (microwave and millimeter-wave) lines with cryogenic filtering and amplification, sufficient DC wiring for device control, and infrastructure to support near-quantum-limited readout.

1. General Requirements

This RFI describes specifications for a dilution refrigerator platform for high-fidelity DC/RF measurements of superconducting circuits at mK temperature. The system must include the following components: (1) A modular, cryogen-free dilution refrigerator that has base temperature < 10 mK and is capable of continuous operation at 20 mK (100 mK) with cooling power ≥ 16 μW (≥ 400 μW) at the mixing chamber (MXC); (2) a fully integrated, 2-stage pulse tube cryocooler that delivers a cooling power ≥ 2.35 W at 4.2 K;

(3) a modular, automated gas handling system (GHS) that is capable of full system diagnostics; (4) modular wiring for DC and RF I/O signals to MXC; (5) various cryogenic electronics ready for quantum circuit measurements; and (6) computerized control hardware/software and thermometry interface. The vendor must provide onsite service that covers system installation, start-up, and training.

2. Principal Configuration

2.1. Cryostat, including:

• A heavy-duty vibration isolation frame for mounting the cryostat, with additional aluminum top plate (~200 kg);

• A fully integrated, closed-cycle two-stage pulse tube cryocooler with cooling powers of ≥ 2.35 W at 4.2 K. Pulse tube to be mounted with edge-welded bellow assembly for reduced vibration amplitude. An additional, internal cold trap is required for extended long-run operation time;

• A dilution unit with base temperature < 10 mK at MXC;

• A thermometry unit that includes temperature controller and 4K heater power supply, with at least 8-channel resistive temperature measurement and at least 4 heater controls operational in manual or close loop modes;

• A resistive heater at the 4K flange for faster warm-up, with at least 40 W rated power and full software integration;

• A Programmable Logic Controller (PLC)-controlled gas handling system (GHS) integrated with booster unit and maintenance-free circulation pump. The GHS shall be capable of full system diagnostics, with full valve position readout, cooling water flowmeter, and uninterruptible power supply for PLC (>1 min);

• A modular, 2-section vacuum can pumped by a turbomolecular pump with a rate ≥ 30 l/s;

• A complete set of magnetic field shields with minimal seams, including (1) a cylindrical, hydrogen-annealed amumetal shield with one end open and one end closed; (2) a cylindrical MXC shield that is attached to the MXC flange, made of gold-plated copper; and (3) a quantum processing unit (QPU) chip carrier for microwave resonator based quantum devices, with performance superior or equivalent to the Quantum Machines Qcage.24 with magnetic shielding.

2.2 Cryogenic wiring, including

• DC installation set:

o RT break-out box with 2x fischer connectors;

o At least 12× twisted pair experimental wiring (35 AWG copper) from RT connector box (24-pin fischer) to 4K flange;

o At least 12× twisted pair experimental wiring (NbTi/CuNi) from 4K flange to the MXC flange;

o Intermediate 25-pin micro-D break-out at the 4K flange;

o Termination with 25-pin micro-D breakout at the MXC flange;

o Additional anchoring to pulse tube and intermediate break-out at 4K shall be included.

• RF installation set (up to 18 GHz):

o Vacuum KF40 installation set with at least 6× hermetic SMA feedthroughs plus 1× aluminum and 1× gold thermal anchoring flanges with F/F SMA bulkheads for 50K and 4K stages;

o Installation set for at least 6× SMA lines from 4K to MXC: gold plated copper thermal anchoring flanges with F/F SMA bulkheads for still, cold plate and MXC.

o At least 6× semi-rigid coaxial lines (18 GHz): RT-4K: 0.86mm SCuNi- CuNi (SMA); 4K-MXC: 0.86mm NbTi-NbTi (SMA).

• Sideloader RF installation set (up to 18 GHz):

o Sideloader installation set with at least 25× hermetic SMA feedthroughs plus 1× aluminum and 1× gold thermal anchoring flanges with F/F SMA bulkheads for 50K and 4K stages;

o Installation set for 25× SMA lines from 4K to MXC: gold plated copper thermal anchoring flanges with F/F SMA bulkheads for still, cold plate and

MXC.

o At least 8× semi-rigid coaxial lines (18 GHz): RT-4K: 0.86mm SCuNi- CuNi (SMA); 4K-MXC: 0.86mm NbTi-NbTi (SMA).

• RF installation set for K-2.92mm lines (up to 40 GHz, KF40):

o Vacuum KF40 installation set with at least 4× hermetic SMA feedthroughs plus 1× aluminum and 1× gold thermal anchoring flanges with F/F K- 2.92mm SMA bulkheads for 50K and 4K stages;

o Installation set for at least 4× K-2.92mm lines from 4K to MXC: gold plated copper thermal anchoring flanges with F/F K-2.92mm bulkheads for still, cold plate and MXC;

o At least 2× semi-rigid coaxial lines (40 GHz): RT-4K: 0.86mm SCuNi- CuNi (K-2.92mm); 4K-MXC: 0.86mm SCuNi-CuNi (K-2.92mm);

o At least 1× semi-rigid coaxial lines (40 GHz): RT-4K: 0.86mm SCuNi- CuNi (K-2.92mm); 4K-MXC: 0.86mm NbTi-NbTi (K-2.92mm).

2.3 Low noise amplifiers (LNA), including

• Amplifier power supply wiring/mounting for at least 8 LNA & IS/CI:

o 8× triple TWP wiring (35 AWG copper) from RT connector box (24-pin fischer) to 4K flange (nano-D) o Bias cable for 1-8 LNAs o Nano-D Clamp 4 AU o 4× mounting beam 80mm AU o 4× mounting bracket 86 mm AU o 16× adapter AU o 16× SMA-SMA coaxial assembly 500 Ohm Cu 2.19, 300mm

• Power Supplies for LNA:

o Low noise linear DC power supplies to support at least cryogenic 5× LNA;

o Input range: 0 ±12V;

o A power block array that support the DC power supplies, with a noise at most 3 mVpk-pk.

• At least 4× cryogenic LNA 4-8 GHz, with performance superior or equivalent to

LNF LNC4_8F.

• At least 1× cryogenic LNA 15-29 GHz, with performance superior or equivalent to

LNF LNC15_29B.

2.4 Microwave readout module, for gain bandwidth 5 GHz to 7 GHz, including:

• Complete cryogenic infrastructure on a side loading tree;

• At least 2× travelling wave parametric amplifier (TWPA);

• Parametric amplifier cold-finger assembly with dual magnetic shield;

• Filtered DC lines for TWPA flux bias control;

• At least 2× low-noise HEMT amplifier;

• DC lines for HEMT amplifier biasing;

• Filtering and isolation microwave components;

• At least 2× pump lines (SCuNi) and at least 2× readout lines (NbTi).

2.5 Control system, including:

• Computer with display;

• Control software with full logging and remote access capability;

• Power distribution unit for GHS and control unit.

2.6 Installation & Services, including:

• Lab layout design;

• System packing, shipping, installation, and commissioning;

• Training for operation and maintenance;

• Warranty: ≥ 24 months (extendable to 36 months), including parts and labor.

3. Performance Requirements This section defines the required features and describes the performance specifications of the proposed dilution refrigerator system. The system should be a fully integrated instrument, including the cryostat, cryocooler and dilution unit, gas handling system, vacuum infrastructure, cryogenic wiring, magnetic shielding, microwave readout, and control electronics. The requirements below should be regarded as minimum specifications; superior performance will be preferred.

3.1 Cryostat and Cryocooler

3.1.1 Temperature range and base temperature. The cryostat shall operate continuously from about 1 kelvin down to below 10 millikelvin at the mixing chamber.

The base temperature must be less than 10 mK at the MXC stage.

3.1.2 Cooling power and refrigerant. The dilution unit shall provide at least 16 μW of cooling at 20 mK, 400 μW at 100 mK, and 575 μW at 120 mK, while requiring no more than 18 NTP liters of helium-3 for operation.

3.1.3 Pulse tube cryocooler. The system must include a closed-cycle pulse tube cryocooler with at least 2.35 W of cooling power at 4.2 K. The pulse tube must be mounted on an edge-welded bellows assembly and supported by a heavy-duty vibration isolation frame with a machined aluminum top plate (~200 kg) to minimize vibration amplitudes at the sample stage.

3.1.4 Cooldown time. The cryostat must achieve cooldown from room temperature to base temperature in no more than 24 hours.

3.1.4 Warm up. A resistive heater of at least 40 W, mounted on the 4K plate and integrated into the system software, shall be available for accelerated warm-up.

3.2 Gas Handling and Vacuum System

3.2.1 Gas handling. The gas handling system (GHS) must be fully PLC-controlled and integrated with the booster unit. It should include a maintenance-free circulation pump, comprehensive diagnostics, full valve position readout, and a cooling water flowmeter. The GHS must also include an uninterruptible power supply capable of maintaining PLC operation for at least one minute during power interruptions.

3.2.2 Vacuum system. The vacuum can shall be a two-section design, evacuated by a turbo pump with a minimum pumping capacity of 30 liters per second. An internal cold trap shall be included to extend operating times between maintenance cycles.

3.3 Sample Space and Magnetic Shielding

3.3.1 Sample space. The sample stage must provide a cylindrical experimental volume sufficient to accommodate modular quantum processor carriers for superconducting devices.

3.3.2 Magnetic shielding. Magnetic interference must be suppressed through a complete set of shields, including:

• a hydrogen-annealed Amumetal cylindrical shield with one end open and one end closed,

• a gold-plated copper shield attached to the mixing chamber, and

• additional shielding surrounding the qubit chip carrier, with performance equivalent or superior to the Quantum Machines Qcage.24 with dual magnetic shields.

3.4 Cryogenic Wiring

3.4.1 DC Wiring. The system shall include at least twenty four (24) twisted-pair copper lines from room temperature to 4 K, and an equivalent number of NbTi/CuNi twisted pairs from 4 K to the mixing chamber. Intermediate breakouts using 25-pin micro-D connectors must be provided at the 4 K and MXC stages. Thermal anchoring to the pulse tube and intermediate stages is required.

3.4.2 RF Wiring up to 18 GHz. The cryostat must be equipped with a dedicated RF installation set to support coaxial lines for experiments up to 18 GHz. A KF40 vacuum flange shall provide at least six (6) hermetic SMA feedthroughs, establishing the room-temperature entry points for the lines. The RF wiring must be routed through two thermally anchored plates, an aluminum plate at approximately 50 K and a gold-plated copper plate at 4 K, where each line is mechanically supported and heat-sunk to reduce thermal conduction into the lower stages. From the 4 K stage to the mixing chamber (MXC), the lines must pass through additional thermal anchoring plates at the Still, Cold Plate, and MXC stages, terminating in SMA bulkheads that allow user access at the experimental platform.

At least six (6) coaxial lines must be fully installed at delivery. The sections from room temperature to 4 K must use 0.86 mm semi-rigid SCuNi–CuNi coaxial cable, while the segments from 4 K to MXC must use 0.86 mm semi-rigid NbTi–NbTi coaxial cable to ensure superconducting transmission at the lowest temperatures. All lines must be specified for frequencies up to 18 GHz and should include attenuators, infrared filters, and low-pass filtering elements at appropriate stages to suppress thermal noise and high-frequency interference.

3.4.3 RF Wiring on sideloader. The system shall include a dedicated sideloader RF assembly that routes a high-density bundle of coaxial lines from room temperature to the cryostat interior. The sideloader vacuum flange must provide no fewer than twenty-five

(25) hermetic SMA feedthroughs, and incorporate two thermally anchored distribution plates, an aluminum plate at the ~50 K stage and a gold-plated copper plate at the 4 K stage, to provide mechanical strain relief and effective heat-sinking for all lines entering through the sideloader. From the 4 K stage to the mixing chamber (MXC), the vendor shall extend these lines through gold-plated copper thermal anchoring plates at the Still, Cold Plate, and MXC stages, terminating at the MXC with suitable SMA bulkheads for experiment connection.

At delivery, a minimum of eight (8) sideloader lines shall be fully installed to the MXC using 0.86 mm semi-rigid SCuNi–CuNi coax from RT to 4 K and 0.86 mm semi-rigid NbTi–NbTi coax from 4 K to MXC. All sideloader lines must be specified and qualified for operation up to 18 GHz, and shall include appropriate attenuation, infrared/low-pass filtering, and thermalization at each intermediate stage to control noise and heat load. The remaining sideloader positions shall be delivered with the hermetic feedthroughs and stage hardware pre-installed, allowing additional lines to be added later without modification of the vacuum boundary or thermal anchoring infrastructure.

3.4.4 High-frequency RF wiring up to 40 GHz. The system shall also provide a high-frequency RF wiring set to enable experiments extending to 40 GHz. This wiring tree must use a KF40 vacuum flange outfitted with at least four (4) hermetic K-2.92 mm feedthroughs. As with the lower-frequency assemblies, the high-frequency lines must be thermalized at intermediate stages using aluminum plates at ~50 K and gold-plated copper plates at 4 K. The lines must continue from the 4 K stage through gold-plated copper anchoring plates at the Still, Cold Plate, and MXC stages, where they will terminate in K-

2.92 mm bulkheads for connection to experimental hardware.

At delivery, the system must include at least two (2) semi-rigid SCuNi–CuNi coaxial lines extending from room temperature to MXC, and at least one (1) semi-rigid NbTi–NbTi coaxial line from 4 K to MXC, to ensure superconducting performance at the base stage.

All lines must be specified for continuous operation up to 40 GHz and should incorporate appropriate attenuation, filtering, and anchoring to control both thermal loading and electromagnetic interference at high frequencies.

3.5 Cryogenic Amplifiers and Biasing

3.5.1 Amplifiers. The system must be equipped with cryogenic amplification to enable high-fidelity readout of superconducting qubits and resonators. At minimum, the cryostat shall support the installation of four (4) low-noise amplifiers operating in the 4–8 GHz frequency band, with performance equivalent or superior to the LNF LNC4_8F. In addition, the system must provide at least one (1) low-noise amplifier covering the 15–29 GHz band, with performance equivalent or superior to the LNF LNC15_29B. These amplifiers must be mounted at the 4 K stage or lower, with appropriate mechanical supports and thermal anchoring to ensure stable operation at cryogenic temperatures.

3.5.2 LNA wiring. The cryostat shall include a complete wiring and support infrastructure to power and bias the cryogenic LNAs. The system must provide wiring capable of supporting at least eight (8) amplifiers or isolator/amplifier chains in parallel.

From room temperature to the 4 K stage, amplifier biasing must be carried by triple twisted-pair copper wiring (35 AWG), routed through Fischer multipin connectors and terminated at nano-D connectors on the 4 K flange. At the 4 K stage, bias lines must be distributed to the amplifier mounting locations through nano-D breakouts, with proper thermal anchoring to intermediate temperature stages to limit parasitic heat load to the dilution unit.

Mechanical hardware, including nano-D clamps, mounting beams, and brackets, must be provided to secure all bias harnesses and amplifier assemblies. Bias cables must be appropriately strain-relieved and thermalized at each stage.

3.5.3 LNA power supplies. The system must also include dedicated low-noise DC power supplies designed for cryogenic amplifier operation. They shall provide adjustable bias voltages and currents with a noise level not exceeding 3 mV peak-to-peak ripple. A modular power block array must be included to support simultaneous operation of at least five (5) amplifiers, with expandability for additional units up to eight (8). They must provide clear monitoring of bias conditions and allow safe shutdown in case of fault.

3.6 Microwave Readout Module

The system must include a microwave readout module operating in the 5–7 GHz band with near-quantum-limited performance. The module shall deliver at least 9 dB improvement in signal-to-noise ratio and include two traveling-wave parametric amplifiers with flux bias control, a dual-shielded cold-finger assembly, at least two cryogenic HEMT amplifiers, and appropriate filtering and isolation components. At least two pump lines (SCuNi) and two readout lines (NbTi) shall be provided.

3.7 Control System and Software

The cryostat must be fully controllable through an industrial computer with an integrated display. Vendor-supplied control software must include a graphical user interface, full data logging, and remote access capability. The thermometry unit must provide at least eight resistive channels and four heater outputs, with manual and closed-loop operation modes. All control and gas handling electronics must be integrated into a dedicated rack with appropriate power distribution and networking.