Research Engineer, Robotics: Physics Simulation and Sim-to-Real

Who You Are:

You are a simulation engineer who makes physics behave. You have written contact and constraint solvers yourself. When a stack jitters, a grasp slips, an object tunnels through a finger or a gripper linkage explodes, you can tell whether the cause is the timestep, constraint softness, the friction model, the joint formulation or the asset itself, and you fix the root cause rather than adding damping until the problem goes away.

You also know that a stable simulator is not the same as a correct one. You treat logged data from real robots as ground truth. You replay the same motion in simulation, look at the residuals, and close the gap with physics you can explain rather than with magic numbers. You want simulation that a robot foundation model can train on at scale, that never blows up at step ten million, and that behaves like the real world when the policy gets there.

Who We Are:

Ai2's Robotics team is led by Dieter Fox. We develop scalable simulation domains to study how robot foundation models scale and generalize, and we build robots that are broadly competent in the real world.

Simulation is central to that mission. We train and evaluate policies across MuJoCo, Isaac Sim/Isaac Lab on Newton, and other GPU simulators, and we deploy them on real bimanual and single-arm manipulators. Whether simulated data is worth anything depends on two things: the simulator must be stable enough to run at scale, and close enough to reality that what is learned there transfers. This role owns both.

Our focus areas include manipulation, large-scale training in simulated environments, sim-to-real transfer, robot foundation models and skill learning. We publish at CoRL, ICRA and RSS, as well as CVPR, ICCV, ECCV, NeurIPS, ICLR and ICML, and we release our models, data and tools openly.

We work closely with other teams across Ai2 and with the University of Washington, only 1.5 miles away.

Your Next Challenge:

The needs below are competencies, not a checklist. If you match many of them but not all, we encourage you to apply.

Stability: Make the Simulator Robust at Scale

• Design, implement and improve contact, friction and constraint solvers: complementarity and soft-constraint formulations, pyramidal versus elliptic friction cones, warm-starting, iteration counts and tolerances.
• Find and remove the failure modes that break large-scale training:




• Jitter in resting contact.
• Interpenetration and tunnelling.
• Energy gain.
• Constraint drift in closed kinematic chains.
• Instability under stiff joint drives.
• Non-determinism across runs and GPUs.




• Make articulated robots and closed loops stable and accurate across MuJoCo, Newton and PhysX: parallel grippers, mimic and coupled joints, tendons. Contribute fixes upstream to those open-source engines.
• Choose integrators, timesteps and substeps with evidence. Show how results change with dt, find where a scene stops converging, and quantify the trade-off between accuracy and throughput for GPU-batched training across thousands of environments.
• Build stress and regression tests for physics: long-horizon rollouts, randomized scenes, extreme parameters and contact-rich edge cases, with failures caught before they reach a training run.
• Make assets simulation-ready: collision geometry, inertial properties, joint limits and contact settings that are stable by construction, consistent across URDF, MJCF and OpenUSD.

Fidelity: Bring Simulated Behaviour Closer to Real

• Fit simulation models to logged hardware data: joint friction (Coulomb, viscous, Stribeck), armature and reflected inertia, payload mass and CoM, actuator drive gains, and latency. Identify what the simulator is missing rather than absorbing it into other parameters.
• Calibrate contact behaviour (stiffness, damping, friction, contact dimensionality, compliance) against recorded pushes, slides, grasps and handovers, so objects slip, stick and settle in simulation as they do on the table.
• Keep the same robot consistent across simulators: one source of truth for frames, masses and contact settings, with MuJoCo, Newton and PhysX agreeing to within millimetres, and every remaining gap explained.
• Own a sim-to-real correlation suite that runs like a test suite:




• Replay recorded trajectories in every simulator.
• Report per-joint RMS, onset lag, velocity profiles and contact-force error against thresholds set in advance.
• Catch regressions whenever a solver, asset or parameter changes.




• Turn measured uncertainty into domain-randomisation ranges for policy training, and measure whether a policy's real-world success tracks its success in the calibrated simulator.
• Write a model card for each robot and scene: every parameter, where it came from and how much to trust it.

What You'll Need:

Minimum Qualifications:

• PhD in robotics, mechanical engineering, applied mathematics, physics, computer graphics or a related field, or a Masters + 3 years of experience. Exceptional candidates with a bachelor's degree and 3+ years of relevant industry experience are also welcome to apply.
• Demonstrated depth in rigid-body dynamics and constrained multibody systems: articulations (reduced and maximal coordinates), contact and friction modelling, and numerical integration of stiff systems.
• Solver or physics-engine code you wrote yourself, in a research codebase, a production engine, or a widely used open-source simulator such as MuJoCo, Newton/Warp, PhysX, Drake, Bullet or Genesis.
• A track record of diagnosing and fixing simulation instability (jitter, penetration, energy drift, divergence), with an understanding of why the fix works.
• Experience fitting simulation parameters to measured data and validating the result quantitatively against real-world recordings.
• Proficiency in Python and C++, experience with robot description formats (URDF, MJCF, OpenUSD), and knowledge of at least one major simulation stack at source level.

Preferred Qualifications:

• GPU programming for physics (CUDA, NVIDIA Warp or JAX) and experience scaling simulation for reinforcement or imitation learning.
• Experience with deformable, cable or FEM simulation (XPBD, VBD, corotational or hyperelastic FEM, Cosserat rods) and its coupling with rigid bodies.
• Familiarity with differentiable simulation, Bayesian or gradient-based parameter estimation, or learned residual dynamics.
• Experience in robot manipulation, grasping or contact-rich tasks, in simulation or on hardware.
• Publications or open-source contributions in simulation, dynamics or sim-to-real transfer (CoRL, RSS, ICRA, SIGGRAPH/SCA, or engine repositories).

Physical Demands and Work Environment:

The physical demands described here are representative of those that must be met by a team member to successfully perform the essential functions of this position. Reasonable accommodations may be made to enable individuals with disabilities to perform the functions.

• Must be able to remain in a stationary position for long periods of time.
• The ability to communicate information and ideas so others will understand. Must be able to exchange accurate information in these situations.
• The ability to observe details at close range.
• Can work under deadlines.

A Little More About Ai2:

Ai2 is a Seattle based non-profit AI research institute founded in 2014 by the late Paul Allen. Our mission is building breakthrough AI to solve the world's biggest problems. We develop foundational AI research and innovation to deliver real-world impact through large-scale open models, data, robotics, conservation, and beyond.

In addition to Ai2's core mission, we also aim to contribute to humanity through our treatment of each member of the Ai2 Team. Some highlights are:

• We are a learning organization - because everything Ai2 does is ground-breaking, we are learning every day. With a wide variety of world-class AI experts as guest speakers, and our commitment to your personal on-going education, Ai2 is a place where you will have opportunities to continue learning alongside your coworkers.
• We value diversity - We seek to hire, support, and promote people from all genders, ethnicities, and all levels of experience regardless of age. We particularly encourage applications from women, non-binary individuals, people of color, members of the LGBTQA+ community, and people with disabilities of any kind.
• We value inclusion - We understand the value that people's individual experiences and perspectives can bring to an organization, and we are building a culture in which all voices are heard, respected and considered.
• We emphasize a healthy work/life balance - we believe our team members are happiest and most productive when their work/life balance is optimized. While we value powerful research results which drive our mission forward, we also value dinner with family, weekend time, and vacation time. We offer generous paid vacation and sick leave as well as family leave.
• We are collaborative and transparent - we consider ourselves a team, all moving with a common purpose. We are quick to cheer our successes, and even quicker to share and jointly problem solve our failures.
• We are in Seattle - and our office is on the water! We have mountains, we have lakes, we have four seasons, we bike to work, we have a vibrant theater scene, and we have so much else. We welcome interest from applicants from outside of the United States.
• We are friendly- chances are you will like every one of the 200+ (and growing) people who work here. We do.

Ai2 is proud to be an Equal Opportunity employer. We do not discriminate based upon race, religion, color, national origin, sex (including pregnancy, childbirth, or related medical conditions), sexual orientation, gender, gender identity, gender expression, transgender status, sexual stereotypes, age, status as a protected veteran, status as an individual with a disability, or other applicable legally protected characteristics. You may view the related Know Your Rights compliance poster and the Pay Transparency Nondiscrimination Provision by clicking on their corresponding links.

This employer participates in E-Verify and will provide the federal government with your Form I-9 information to confirm that you are authorized to work in the U.S. If E-Verify cannot confirm that you are authorized to work, this employer is required to give you written instructions and an opportunity to contact the Department of Homeland Security (DHS) or Social Security Administration (SSA) so you can begin to resolve the issue before the employer can take any action against you, including terminating your employment. Employers can only use E-Verify once you have accepted a job offer and completed the Form I-9.

We are committed to providing reasonable accommodations to employees and applicants with disabilities to the full extent required by the Americans with Disabilities Act (ADA). If you feel you need a reasonable accommodation pursuant to the ADA, you are encouraged to contact us at recruiting@allenai.org.

Benefits:

• Team members and their families are covered by medical, dental, vision, basic life insurance, basic accidental death and dismemberment insurance, short-term disability, long-term disability, and an employee assistance program.
• Team members are able to enroll in our voluntary life insurance program, our voluntary accidental death and dismemberment program, our health savings account plan, our healthcare reimbursement arrangement plan, and our health care and dependent care flexible spending account plans.
• Team members are able to enroll in our company's 401k plan.
• Team members will receive $125 per month to assist with commuting or internet expenses and will also receive $200 per month for fitness and wellbeing expenses.
• Team members will also receive up to ten sick days per year, up to seven personal days per year, up to 20 vacation days per year and twelve paid holidays throughout the calendar year.
• Team members will be able to receive annual bonuses and can participate in the long-term incentive plan.

Note: This job description in no way states or implies that these are the only duties to be performed by the team members(s) of this position. Team members will be required to follow any other job-related instructions and to perform any other job-related duties requested by any person authorized to give instructions or assignments. All duties and responsibilities are essential functions and requirements and are subject to possible modification to reasonably accommodate individuals with disabilities. To perform this job successfully, the team member(s) will possess the skills, aptitudes, and abilities to perform each duty proficiently. Some requirements may exclude individuals who pose a direct threat or significant risk to the health or safety of themselves or others. The requirements listed in this document are the minimum levels of knowledge, skills, or abilities. This document does not create an employment contract, implied or otherwise, other than an at will relationship.