MEMS program for LOUD

K.Stifter, H. Magoon, D. Baxter, others

8/25/2022

Overview

To provide background/context, we start with:

1. Reminder of MEMS functionality
2. Recap of Lab A program

Thinking about LOUD, tests can be split into two categories:

• MEMS commissioning
1. This encompasses anything with demonstration of full functionality of MEMS mirror and setup.
• Science goals
• This encompasses any dark matter- or detector performance-related topics that bring us closer to realizing a quantum sensor-based DM detector.

Schematic of MEMS system

Detailed list of requirements can be found here

Eventually, made of a chopping unit and a steering unit

Steering unit is only thing being worked on at FNAL, chopping unit is at SLAC

MEMS mirrors

Cryogenic movement is hard due to:

• Power dissipation
• Freeze out of movement mechanisms/control

Our solution: modified MEMS mirrors (right)

Good because:

• High broadband reflectance (aluminized)
• Relatively large deflection angles (+/-5°)
• “No power dissipation while stationary”
• Modification: Al deposition over doped Si control lines for low-T operation

Steering unit design

Focusing optics

Stationary mirror

To device

From optical fiber

There is no MEMS “readout” - we can only control the voltages we put in, which angles the mirror (and steers the laser)

Steering unit output

Focusing optics

Stationary mirror

To device

From optical fiber

All very passive! We have no feedback on where the laser is without the readout of an attached device

Device attachment

1. Housing is designed

2. Device is mounted

3. Cover is designed

4. Device is secured at MEMS output

Note: Most housings do not need to be redesigned, but a new cover has to be designed for each new housing

Mounting of MEMS system in fridge

MEMS unit screwed to MC plate. Filter installed at output.

MEMS electrical connection at the bottom, SMA connections on device housing. Optical connection on other side.

It has a very large footprint in the fridge.

Recap: Lab A program

Overall: Show that the MEMS mirror and associated setup works - that it functions while cold and operates as expected.

Major goals:

1. Determine the effect of laser power on fridge temperature - largely done
2. Determine the effect of MEMS operation on fridge temperature - largely done
3. Determine conclusively if the MEMS is moving while cold - in progress

Possible future goals:

1. Refine MEMS steering
2. Measure in situ spot size, position resolution
3. Practice varying laser power/timing to produce different pulse types

Commissioning goals + measurement plans

List of LOUD MEMS commissioning goals

Determining the laser position in situ: ideally

Scanning area

Qubit chip

Qubits

Laser off chip: no response

Determining the laser position in situ: ideally

Scanning area

Qubit chip

Qubits

Laser on chip but off qubit: some response

Determining the laser position in situ: ideally

Scanning area

Qubit chip

Qubits

Laser on qubit: different response

Determining the laser position in situ: ideally

Scanning area

Qubit chip

Qubits

As we sweep across chip, can track physical XY location on chip by looking at response from qubits, get linear mapping across whole chip

Want to do this in situ, because behavior might change between warm/cold

Determining the position resolution in situ: ideally

Scanning area

Qubit chip

Qubits

We can repeatedly target a qubit (or other small structure) to see if we get a repeatable behavior (and therefore position)

Determining the position resolution in situ: ideally

Scanning area

Qubit chip

Qubits

We can repeatedly target a qubit (or other small structure) to see if we get a repeatable behavior (and therefore position)

Determining the spot size in situ: ideally

Scanning area

Qubit chip

Qubits

This one I am less concerned about, because I don’t see it changing much warm->cold…

But we can target the edge of a structure, and watch response as spot size goes up/down.

Determining the spot size in situ: ideally

Scanning area

Qubit chip

Qubits

This one I am less concerned about, because I don’t see it changing much warm->cold…

But we can target the edge of a structure, and watch response as spot size goes up/down.

Determining the laser position in situ: if needed

What if we don’t see the expected response?

Scanning area

Qubit chip

Qubits

We can design a screen with irregular hole pattern in it, and try to see the response when we target a hole/not a hole

Science goals

Big picture QSC science goals (my understanding)

Ultimately: Want to create a DM detector with lowest threshold possible, a reasonable exposure, and some level of background control/rejection/understanding

• Trying to do that using quantum sensors

(Some) components of this goal:

• Understanding of how we can detect energy deposits using quantum sensors
• Detector performance, calibration over volume
• Optimization of detector design
• Energy threshold
• Understanding of backgrounds, what signals they generate

List of science goals that can be tackled with MEMS

Rough paper planning (based on MEMS results)

A MEMS technology paper? - 2022?

• SPIE?

An “energy deposition location” paper - 2023?

• Hope would be to understand definitively the sensing mechanism
• Can explore phonon transport properties
• Some level of detector performance parameters, calibration over volume
• Significant simulation component

A “detector threshold” paper - 2024?

• Exploring possible energy spectrum
• Differences between different types of interactions - maybe a theory component? Could lead to backgrounds prediction/rejection. Or is this a separate paper?
• Ultimately, determine smallest amount of detectable energy

Qubit design papers? - As possible?

• Probably in collaboration with Wisconsin, Purdue, SLAC, whoever else has ideas on device design that we can then test.

​

Other thoughts/questions

Are those papers too beefy? Should we be thinking about smaller, bite-sized papers?

• General question for anyone familiar with publication culture

How do these tie into other QSC publications/plans?

• Question for QSC management

How do we tie these results back into QIS? How are they useful to that community?

• I can think about this question in the future