Berlin 2001 – scientific programme
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Q: Quantenoptik
Q 25: Quantum Effects II
Q 25.3: Talk
Thursday, April 5, 2001, 16:15–16:30, H 3010
Let’s ascertain the values of σx, σy, and σz of a spin-1/2 particle. — •Markus Weber1, Oliver Schulz1, Ruprecht Steinhübl1, Berthold-Georg Englert2, Christian Kurtsiefer1, and Harald Weinfurter1,2 — 1Sektion Physik, LMU, München — 2Max-Planck-Institut für Quantenoptik, Garching
In 1987 Vaidman, Aharonov, and Albert (VAA) showed how to “retrodict” the outcome of a spin measurement (+1/2 or −1/2) without knowledge of the basis (x, y or z) in which it was performed [1]. The key for the solution of this task is to entangle the to-be-measured particle with an external particle. We realize this experiment using entanglement between two degrees of freedom (polarization and time or space) of a single photon. Alice prepares a polarization-time-entangled state with an asymmetric Mach-Zehnder-interferometer (MZI). Then Bob performs an arbitrary projective spin measurement on the polarization degree of freedom in one of the three noncommuting bases (H ↔ V), (R ↔ L) or (+45∘↔ −45∘). To retrodict the result of Bob’s spin measurement with certainty, Alice finally has to project the state of the photon on four entangled eigenstates. We show first experimental results of the state preparation and the VAA-state analysis.
[1] L. Vaidman, Y. Aharonov, D. Z. Albert, Phys. Rev. Lett. 58(14), 1385 (1987)