Schematic Symbols for Quantum Logic Gates (in clockwise order) -Hadamard Gate, Pauli X (Not) Gate, Pauli Y Gate, Pauli Z Gate.

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... we turn to our main proposal, where we implement an improved version of Deutsch's Algorithm. Instead of running the purification algorithm on 2 pairs, we can apply it on Fig. 11. Schematic illustration of a generalised entanglement purification scheme using n imperfect Bell pairs, local operations and classical communication. multiple pairs at the same time. For instance, the 5-qubit variant can purify 5 imperfect pairs with a fidelity of 0.85 into one with a fidelity above 99% in a single round with a success ...

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... Quantum-Circuit for a 3-qubit variant of the improved Deutsch Algorithm is shown in Fig.10. A schematic for extending the algorithm to multiple qubits is given in Fig. 11. ...

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... Quantum-Circuit for a 3-qubit variant of the improved Deutsch Algorithm is shown in Fig.10. A schematic for extending the algorithm to multiple qubits is given in Fig. ...

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... so the correction operation can be performed. Further the message heralds the success or failure of the swapping operation if necessary. This is essentially equivalent to Teleportation protocol, but, the qubit whose state is to be transferred is entangled with another qubit. The quantum circuit for the Entanglement Swapping Protocol is shown in Fig. ...

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... that we have described the fundamental components needed for quantum repeaters, it is insightful to illustrate how they are combined together (see Fig. 13) and the quantum repeaters perform. Let us consider this in general before moving to specific approaches. Our task begins by the creation of a number of entangled links between adjacent repeater nodes. Once enough links have been generated entanglement purification is performed if necessary (either once or a number of times) to give ...

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... the entanglement one requires between the Alice and Bob's nodes with the required fidelity. If the purification or entanglement swapping fails at any step, we must start over that part again from round 0. After the entire pipeline of operations is complete, a robust and reliable entangled link will be established between the two parties. Fig. 13. Quantum repeater scheme for generating long-range entanglement. It begins by splitting the network into a number of segments and placing repeater stations at these nodes. Multiple entangled pairs are then generated between adjacent nodes. These links are then purified and entanglement swapping is performed to create a link twice as ...

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... the reliability of producing Bell-states at two different circuit-nodes of the devices was benchmarked. The ciruit of Fig. 4 was used to do this. But, the qubits were measured in the Bell-basis instead of the computational-basis. The results obtained after executing the circuit 5000 times in the local simulator, and, the IBMQ devices are shown in Fig. 14. For a perfect Bell-state |Φ + , perfect gates and perfect measurement, the output should be 00 with probability 1. Imperfections in any of these operations or due to information leakage will give rise to spurious outputs. As can be seen, the [ibmq_16_melbourne] is the most noisy device with an output fidelity of about 85.4%, while ...

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... we simulate the effect of channel-length on entanglement distribution. The channel is emulated by repeatedly applying SWAP gate to send qubits from the transmitter to the receiver [30]. This is illustrated in Fig. 15, in which a channel with 3 SWAP operations is shown. The performance of the devices for this Quantum Channel is shown in ...

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... results of the Entanglement Swapping protocol with one repeater node in the middle is shown in Fig. 18. As can be seen, the swapping protocol establishes much higher fidelity entanglement than would be possible by directly transferring the ...

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... 3-node Qauntum Repeater integrating all the elements and algorithms discussed until now, is shown in Fig. 20. Even with only 3 nodes, the circuit surpasses the qubit-count to be reliably executed in an IBMQ device. Thus, it was simulated natively on a local device. The simulation results indicating the performance of the architecture is shown in Fig. ...

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... is much scope to extend this work even further. A promising direction is to come up with robust and condense Error-Correcting Codes, so that, the fidelity may be increased without discarding all the bell-pairs. This will result in higher yield-rates without sacrificing the error-rates. In the current Fig. 16. Simulation Results for Channel-Length on [ibmqx4]. No. of Swap Gates -(a) 1, (b) 2, (c) 3. It is clearly seen that, the fidelity falls below 50% for just 3 SWAP Gates, rendering the Bell-Pair useless. This demonstrates the severe effects of noise and imperfect hardware on Quantum Communication. form, as our experiments demonstrate, ...