Abstract
Quantum key distribution protocols typically make use of a one-way quantum channel to distribute a shared secret string to two distant users. However, protocols exploiting a two-way quantum channel have been proposed as an alternative route to the same goal, with the potential advantage of outperforming one-way protocols. Here we provide a strategy to prove security for two-way quantum key distribution protocols against the most general quantum attack possible by an eavesdropper. We utilize an entropic uncertainty relation, and only a few assumptions need to be made about the devices used in the protocol. We also show that a two-way protocol can outperform comparable one-way protocols.
Highlights
Quantum key distribution (QKD) research has been primarily focused on one-way protocols: One party, Alice, prepares states, sends them through an insecure quantum channel, and another party, Bob, does a measurement [1,2]
One motivation is that some two-way protocols are deterministic, that is, they do not require any sifting of the raw keys generated due to a mismatch of basis choices
Bob needs to flip his raw bit for each signal that he used the X basis and Alice announces she applied an encoding from S1. We purify these two prepare and measure QKD protocols by showing that they are equivalent to protocols that start with entangled states distributed by Eve followed by measurements by Alice and Bob
Summary
Quantum key distribution (QKD) research has been primarily focused on one-way protocols: One party, Alice, prepares states, sends them through an insecure quantum channel, and another party, Bob, does a measurement [1,2]. In the last decade, two-way protocols have been proposed where Bob prepares states, sends them to Alice through an insecure quantum channel, Alice does an encoding on the states, sends them backwards through the same quantum channel, and Bob performs a measurement [3,4,5,6,7] Paradigmatic examples of these kind of protocols are the so-called “Ping-Pong” protocol [6] and the LM05 protocol [7]. Using this uncertainty relation and the Devetak-Winter security bound [30], we demonstrate how to prove security against the most general type of attacks for two-way protocols We use this method to prove security for two example protocols: a super dense coding (SDC) protocol similar to the Ping-Pong protocol [6] and a protocol similar to LM05 (which we will refer to as LM05) [7]. We compare the key rates to different implementations of the BB84 protocol
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