Abstract
Measurement-Device-Independent Quantum Key Distribution (MDI-QKD) is a two-photon protocol devised to eliminate eavesdropping attacks that interrogate or control the detector in realized quantum key distribution systems. In MDI-QKD, the measurements are carried out by an untrusted third party, and the measurement results are announced openly. Knowledge or control of the measurement results gives the third party no information about the secret key. Error-free implementation of the MDI-QKD protocol requires the crypto-communicating parties, Alice and Bob, to independently prepare and transmit single photons that are physically indistinguishable, with the possible exception of their polarization states. In this paper, we apply the formalism of quantum optics and Monte Carlo simulations to quantify the impact of small errors in wavelength, bandwidth, polarization and timing between Alice’s photons and Bob’s photons on the MDI-QKD quantum bit error rate (QBER). Using published single-photon source characteristics from two-photon interference experiments as a test case, our simulations predict that the finite tolerances of these sources contribute ( 4.04 ± 20 / N sifted ) % to the QBER in an MDI-QKD implementation generating an N sifted -bit sifted key.
Highlights
Quantum Key Distribution (QKD) is an application of quantum cryptography—the process of exploiting quantum effects to establish secure communications between two authorized users, Alice and Bob, in the presence of an unwanted third party, Eve
The fraction of bits discarded due to opposite basis selection or unusable measurement results are in line with expectations—approximately 25% of the raw key bits are retained in the sifted key
By simulating the Measurement-Device-Independent Quantum Key Distribution (MDI-QKD) protocol using photon source tolerances from a well-characterized two-photon interference study, we demonstrate both good agreement with experiment and the ability to relate the achievable visibility to fluctuations in specific photon properties
Summary
Quantum Key Distribution (QKD) is an application of quantum cryptography—the process of exploiting quantum effects to establish secure communications between two authorized users, Alice and Bob, in the presence of an unwanted third party, Eve. Alice and Bob publicly announced which polarization basis (horizontal-vertical or antidiagonal-diagonal) they used for encoding. From this information and their private knowledge of their own photon encodings, Alice and Bob can infer one bit of shared secret key in 25% of the exchanges under ideal circumstances. Despite its immunity from eavesdropping attacks on the detector, MDI-QKD is susceptible to physical non-idealities that can limit the key generation rate by introducing quantum bit errors, which are physically indistinguishable from perturbations caused by Eve’s measurements [9]. In addition to detector inefficiencies, dark count rates [10] and polarization errors, MDI-QKD is susceptible to bit errors caused by timing differences [7] and photon distinguishability in pulse envelope, bandwidth and wavelength [11].
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