v3.26.1
Cover - shares
 6 Months Ended
Jun. 30, 2026
Aug. 11, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-39486  
Entity Registrant Name QUANTUM-SI INCORPORATED  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 85-1388175  
Entity Address, Address Line One 29 Business Park Drive  
Entity Address, City or Town Branford  
Entity Address, State or Province CT  
Entity Address, Postal Zip Code 06405  
City Area Code 866  
Local Phone Number 688-7374  
Title of 12(b) Security Class A common stock, $0.0001 per share  
Trading Symbol QSI  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Central Index Key 0001816431  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Class A common stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   198,946,412
Class B common stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   19,937,500