Quantum Teleportation with a Quantum Dot Single Photon Source

We report the experimental demonstration of a quantum teleportation protocol with a semiconductor single photon source. Two qubits, a target and an ancilla, each defined by a single photon occupying two optical modes (dual-rail qubit), were generated independently by the single photon source. Upon measurement of two modes from different qubits and postselection, the state of the two remaining modes was found to reproduce the state of the target qubit. In particular, the coherence between the target qubit modes was transferred to the output modes to a large extent. The observed fidelity is 80%, in agreement with the residual distinguishability between consecutive photons from the source. An improved version of this teleportation scheme using more ancillas is the building block of the recent Knill, Laflamme, and Milburn proposal for efficient linear optics quantum computation.

Figure 1

Schematic of single mode teleportation. Target and ancilla qubits are each defined by a single photon occupying two optical modes (1-2 and 3-4). When detector C records a single photon, the state in modes 1-4 reproduces the initial state of the target. In particular, the coherence between modes 1-2 of the target can be transferred to a coherence between modes 1-4.

Figure 2

Experimental setup. All the beam splitters (BS) shown are 50-50 nonpolarizing BS. The teleportation procedure works when the ancilla photon is delayed, but the target is not. After preparation, the target photon occupies modes 1 and 2, and the ancilla occupies modes 3 and 4. Modes 2 and 3 are mixed at BS 1 and subsequently measured by detectors C and D, this step being the heart of the teleportation. When C records a single photon, another single photon occupies modes 1-4 (output qubit). The phase coherence between modes 1-4 in the output state is measured by mixing those modes at BS 2 and recording single counts at detector A or B. Note that since an event is recorded only if A and C or B and C clicked, more than one photon could not have reached detector C.

Figure 3

Typical correlation histograms taken simultaneously between detectors $\mathrm{A}/\mathrm{C}$ and $\mathrm{B}/\mathrm{C}$. The central region indicated by the dashed lines corresponds to the postselected events, when target and ancilla photons had such a timing that it is impossible to distinguish between them based on the time of detection. As the path length $\Delta$ varies, so does the relative size of the central peaks for detectors A and B. The sum of count rates for the central peaks of detector A and B was $800/\mathrm{s}$, independently of $\varphi$ as shown in Fig. 4.

Figure 4

Verification of single mode teleportation. Coincidence counts between detector A/C and B/C are plotted for different voltages applied to the piezo transducer, i.e., for different path length $\Delta$ of mode 1. The observed modulation of the counts implies that the initial coherence contained in the target qubit was transferred to a large extent to the output qubit. The reduced contrast ($\sim 60\%$) is principally due to imperfect indistinguishability between the target and ancilla photons.