Quantum Teleportation with a Three-Bell-State Analyzer

We present a novel Bell-state analyzer (BSA) for time-bin qubits allowing the detection of three out of four Bell states with linear optics, two detectors, and no auxiliary photons. The theoretical success rate of this scheme is 50%. Our new BSA demonstrates the power of generalized quantum measurements, known as positive operator valued measurements. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a fidelity larger than the cloning limit.

Figure 1

A schematic representation of the new type of Bell-state measurement. When two qubit states are sent into a time-bin interferometer the output state is a mixture of photons in two directional modes and three temporal modes. By looking at certain combinations of these photons a Bell-state measurement can be performed for three different Bell states.

Figure 2

A rough overview of the experimental setup. The fiber interferometers shown here are in reality Michelson interferometers; for the interferometer in the BSA two circulators are used to have two separate inputs and outputs. Not shown in the figure is the method used for stabilizing the interferometers.

Figure 3

Left: The result of the 1-Bell-state teleportation experiment (a beam splitter instead of the interferometer) with $F_{\mathrm{raw}}=79\%$ and $F_{\mathrm{net}}=91\%$. Right: A typical result of the scan in delay of the coincidences “00” and “22”. The predicted antidip is clearly visible in both curves with a visibility after noise substraction of 32% for “0” on D1 and D2 and 26% for “2” on D1 and D2 ($\mathrm{\text{theoretical maximum}}=1/3$ [22]).

Figure 4

These graphs show the interference fringes found when scanning the interferometer at Bob. we found visibilities of 0.22,0.43 and 0.38 for $|{\psi }_{+}⟩$, $|{\varphi }_{+}⟩$ and $|{\psi }_{-}⟩$. The average visibility of the BSA is $V_{\mathrm{avg}}=0.34$ ($F=0.67$).

Figure 5

This graph shows two measurements that were taken with a different value of $\delta$. The closed datapoints correspond to a measurement with $\delta$ equal to $-\beta$. The open points are for a $\delta$ which was shifted by $35\pm 5°$. There is a clear shift of the fringe for $|{\varphi }_{+}⟩$ by 74° with regards to the other fringes which corresponds to the expected value of $70\pm 10°$.