PPubMed5 Jul 2016Cited 72×

Purification of Logic-Qubit Entanglement

Lan Zhou, Yu-Bo Sheng

Abstract

Recently, the logic-qubit entanglement shows its potential application in future quantum communication and quantum network. However, the entanglement will suffer from the noise and decoherence. In this paper, we will investigate the first entanglement purification protocol for logic-qubit entanglement. We show that both the bit-flip error and phase-flip error in logic-qubit entanglement can be well purified. Moreover, the bit-flip error in physical-qubit entanglement can be completely corrected. The phase-flip in physical-qubit entanglement error equals to the bit-flip error in logic-qubit entanglement, which can also be purified. This entanglement purification protocol may provide some potential applications in future quantum communication and quantum network.

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First protocol to purify logic‑qubit entanglement, removing both bit‑flip and phase‑flip errors and correcting physical‑qubit errors.

What’s new

i.Proposes the first entanglement purification protocol (EPP) for logic‑qubit entanglement
ii.Demonstrates purification of both bit‑flip and phase‑flip errors in logic‑qubit entanglement
iii.Shows local correction of bit‑flip errors in physical qubits
iv.Extends the method to arbitrary N‑particle GHZ‑encoded logic qubits
v.Analyzes feasibility with deterministic CNOT‑gate technologies

How they did it

The authors design a theoretical protocol that uses controlled‑NOT (CNOT) and Hadamard gates to map logic‑qubit errors onto physical‑qubit errors, then apply known physical‑qubit purification steps. By processing two copies of mixed states and measuring ancillary qubits, they obtain a higher‑fidelity entangled pair. Fidelity improvement is quantified by probabilities such as F² for successful purification.

What they found

Successful purification occurs with probability F², yielding a new fidelity F′ > F
Bit‑flip errors in physical‑qubit entanglement can be completely corrected locally
Phase‑flip errors are transformed into bit‑flip errors and purified with the same protocol
The scheme works for any N‑particle GHZ‑encoded logic qubit

Caveats

✕Requires high‑fidelity, possibly deterministic CNOT gates that are not yet experimentally demonstrated
✕Analysis assumes ideal operations without accounting for realistic noise in gates and measurements
✕Only a theoretical proposal; experimental validation is pending

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