Applied Physicist - Quantum RF Sensing (Qss)

Infleqtion is a global quantum technology company solving some of the world’s most challenging problems. We build and integrate quantum computers, sensors, and networks. From fundamental physics to leading-edge commercial products, Infleqtion enables “quantum everywhere” through an ecosystem of devices and platforms. 

Quantum Spectrum, also known as QRF, develops fieldable radio-frequency sensing systems based on Rydberg atoms. The team combines atomic physics, lasers and photonics, RF electronics, embedded controls, software, and precision hardware to turn laboratory prototypes into repeatable, integrated sensing systems. 

Position Summary 

Infleqtion is seeking an Applied Physicist to build, operate, and improve experimental platforms for Rydberg-atom radio-frequency sensing. Reporting to the Director of R&D, Quantum RF, this physicist will independently own defined experiments and testbeds under senior technical direction, translate atomic, optical, and RF behavior into measurable sensor improvements, and carry validated improvements into integrated QRF systems. The role is centered on hands-on laboratory work; modeling supports experiment design and interpretation rather than serving as the principal output. 

Job Responsibilities 

The duties and responsibilities below describe the essential functions of the role. Depending on business needs, the position may perform some or all these duties. Duties, responsibilities, and activities may change, or new ones may be assigned at any time with or without notice. 

• Own defined experimental campaigns addressing QRF sensitivity, noise, stability, bandwidth, dynamic range, and repeatability. 

• Build, align, commission, operate, maintain, and troubleshoot persistent testbeds that integrate lasers and optics, atomic-sensing hardware, RF and electronic instrumentation, controls, and data acquisition. 

• Design and execute controlled experiments that isolate performance limitations and convert results into specific hardware, operating-point, calibration, or control-system improvements. 

• Integrate validated experimental improvements into sensor heads, subsystems, and complete QRF systems; verify performance against quantitative requirements and documented test methods. 

• Characterize vapor cells and RF resonators, including thermal, optical, geometric, material, field-delivery, and repeatability effects that influence sensor performance. 

• Establish and maintain laser-frequency locks, optical-power stability, photodetection, and associated noise-characterization methods. 

• Calibrate and characterize RF delivery through electrodes, resonators, antennas, TEM or GTEM cells, and related test configurations using appropriate RF and microwave instrumentation. 

• Develop automated instrument-control, parameter-sweep, optimization, calibration, and data-analysis workflows using Python or comparable scientific tools. 

• Analyze experimental data with appropriate uncertainty, noise, and repeatability treatment; use atomic, optical, or electromagnetic models to guide experiments, interpret results, and investigate discrepancies among predicted, benchtop, subsystem, and integrated-system performance. 

• Translate findings into design recommendations, configuration records, test procedures, technical reports, and verification evidence that engineers and technicians can reproduce. 

• Work with RF, optical-mechanical, electrical, embedded-software, systems, and technician personnel to make experimental configurations stable, maintainable, and transferable. 

• Provide occasional support for laboratory or field demonstrations and customer-program testing as assigned, following applicable safety, export-control, configuration-control, and documentation requirements. 

Requirements

• Bachelor’s degree in physics, applied physics, optical engineering, electrical engineering, or a closely related field plus at least four years of relevant hands-on experimental experience; a master’s degree plus at least two years; or a PhD with directly relevant experimental research. Equivalent combinations of education and experience will be considered. 

• Demonstrated hands-on experience personally building, aligning, operating, and troubleshooting complex experimental apparatus that integrates two or more of the following: lasers or optics, electronics, RF or microwave hardware, thermal or mechanical hardware, and software or controls. 

• Practical experience with laser and optical alignment, photodetection, electronic instrumentation, and diagnosis of noise, stability, or performance limitations. 

• Working knowledge of RF measurements and experience using equipment such as signal generators, spectrum analyzers, oscilloscopes, or vector network analyzers. 

• Ability to design controlled experiments, analyze noisy data, assess measurement uncertainty and repeatability, and draw defensible conclusions from incomplete or conflicting results. 

• Experience automating experiments and analyzing data using Python or a comparable scientific programming environment. 

• Ability to independently plan and execute defined laboratory work, document results clearly, and collaborate across physics, engineering, and product disciplines while seeking senior direction for broader architecture and scientific strategy. 
• Comfortable working in a fast-moving environment where designs, schedules, and supplier constraints evolve quickly.  

Preferred Qualifications 

• Hands-on experience with Rydberg atoms, electromagnetically induced transparency, Autler–Townes spectroscopy, atomic RF electrometry, or closely related vapor-cell sensing is strongly preferred. 

• Experience with rubidium or cesium vapor cells, multi-laser spectroscopy, acousto-optic or electro-optic modulators, optical-frequency locking, optical-power stabilization, or low-noise photodetection. 

• Experience characterizing RF resonators, calibrated RF-field delivery, antennas, electrodes, TEM or GTEM cells, or microwave measurement systems. 

• Experience integrating precision laboratory instruments into stable, repeatable, transportable, or field-capable systems. 

• Familiarity with requirements-based verification, configuration-controlled hardware, and test evidence for aerospace, defense, scientific-instrumentation, or U.S. government programs; a current or previously held U.S. government security clearance is preferred but not required. 

• Experience using Ansys HFSS, COMSOL, Zemax, Rydiqule, or related modeling tools to design or interpret experiments. 

Working Conditions and Physical Requirements 

Work is performed primarily on site in laboratory, office, and integration/test environments and involves work around laser systems, RF and microwave equipment, electronic test equipment, heated vapor-cell hardware, optical tables, tools, and precision instrumentation. Required personal protective equipment will be provided and must be used in accordance with company requirements. With or without reasonable accommodation, the role requires the ability to work at laboratory benches for extended periods, perform fine optical and electronic alignment and adjustment tasks, and occasionally lift and carry laboratory equipment or components weighing up to forty pounds. Up to 10% of travel may be required. 

Benefits

• Salary Range: per year 145000-170000
• 100% company-paid medical, dental, vision, short/long-term disability  
• Employer-funded Health Savings Account  
• Unlimited PTO  
• 401(k) match  
• Company-paid Life and AD&D Insurance  
• Flexible Savings Account  
• Paid FMLA, Maternity/Paternity Leave  
• Employee Assistance Program  
• Student Loan Repayment 
• Equity Program

Notice to Recruitment Agencies:

Infleqtion does not accept unsolicited resumes from agencies. Infleqtion is not responsible for any fees related to unsolicited resumes.