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We experimentally demonstrate that tomographic measurements can be performedfor states of qubits before they are prepared. A variant of the quantumteleportation protocol is used as a channel between two instants in time,allowing measurements for polarisation states of photons to be implemented 88ns before they are created. Measurement data taken at the early time and laterunscrambled according to the results of the protocol's Bell measurements,produces density matrices with an average fidelity of $0.90 \pm 0.01$ againstthe ideal states of photons created at the later time. Process tomography ofthe time-reverse quantum channel finds an average process fidelity of $0.84 \pm0.02$. While our proof-of-principle implementation necessitates somepost-selection, the general protocol is deterministic and requires nopost-selection to sift desired states and reject a larger ensemble.

Taking tomographic measurements for photonic qubits 88 ns before they are created