2016/04/30 by G. S. Thekkadath, Guillaume Thekkadath, Lambert Giner +9 · 4 citations
Chemistry · Computer Science · Physics and Astronomy · #Chemistry #Cold Atom Physics and Bose-Einstein Condensates #Computational physics #Computer science #Density matrix #Materials science #Matrix (chemical analysis) #Measure (data warehouse) #Observable #Photon #Physics #Polarization (electrochemistry) #Quantum #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum mechanics #Quantum state #Quantum tomography #Statistical physics #Weak measurement #quant-ph
paper · pdf · doi:10.1103/physrevlett.117.120401
published as Phys. Rev. Lett. 117, 120401 (2016) · 5 pages, 3 figures. Updated and includes SM (6 pages, 2 figures)
arxiv created 2016/09/12 · openalex publication_date 2016/09/12 · arxiv updated 2016/09/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
One drawback of conventional quantum state tomography is that it does not readily provide access to single density matrix elements since it requires a global reconstruction. Here, we experimentally demonstrate a scheme that can be used to directly measure individual density matrix elements of general quantum states. The scheme relies on measuring a sequence of three observables, each complementary to the last. The first two measurements are made weak to minimize the disturbance they cause to the state, while the final measurement is strong. We perform this joint measurement on polarized photons in pure and mixed states to directly measure their density matrix. The weak measurements are achieved using two walk-off crystals, each inducing a polarization-dependent spatial shift that couples the spatial and polarization degrees of freedom of the photons. This direct measurement method provides an operational meaning to the density matrix and promises to be especially useful for large dimensional states.