Protocol Index

A protocol specifies what parties can do, what they initially share, which messages they exchange, and what output they obtain. This index makes those resource and trust conditions explicit. The linked pages explain the derivations and security assumptions; a protocol name alone is not a security proof for a device implementation.

Communication and entanglement conversion

The first two rows describe ideal, noiseless, deterministic qubit protocols. An ebit is a shared Bell pair; a cbit is a transmitted classical bit; a qubit channel transmits an arbitrary qubit state.

Protocol	Resources, output, and conditions
Quantum Teleportation	One ebit plus two cbits from sender to receiver transmit one unknown qubit state. Consumes the entangled pair; correction requires the classical record.
Superdense Coding	One ebit plus one transmitted qubit convey two chosen cbits. Entanglement must already be distributed and the receiver must perform the joint decoding measurement.
Entanglement Swapping	Two links sharing an intermediate node become an end-to-end entangled link after a joint measurement. Heralding and outcome-dependent frame information must reach the endpoints; implementation success can be probabilistic.
Entanglement Distillation	Several noisy shared pairs plus local operations and classical communication (LOCC) produce fewer higher-quality pairs. Yield and feasibility depend on the input state and whether classical communication is one-way or two-way.
Quantum Repeaters	Link generation and connection, with storage, distillation or error correction as required by the architecture, establish remote entanglement. Rate depends on loss, local operations, multiplexing, and architecture-specific waiting or storage costs.

All-photonic repeater constructions, such as that of Azuma, Tamaki, and Lo, avoid long-lived matter memories at intermediate stations; optical resources and synchronization remain necessary.

Write $[qq]$ for one ebit, $[c\to c]$ for a classical bit channel, and $[q\to q]$ for a qubit channel, with each channel directed from sender to receiver. The standard resource statements are

$$\begin{aligned} 1\ [qq]+2\ [c\to c]&\succeq1\ [q\to q],\\ 1\ [qq]+1\ [q\to q]&\succeq2\ [c\to c]. \end{aligned}$$

The relation means that the resources on the left implement the task on the right under the ideal assumptions. It is not an equation allowing unrestricted cancellation of resources. See Communication with Quantum Systems for the resource language.

Key distribution, randomness, and delegation

Protocol or family	Task and trust assumptions
BB84	Nonorthogonal preparations and complementary measurements generate correlated raw data, followed by parameter estimation and classical processing. Requires authenticated classical communication and a source/detector model or a security proof covering their imperfections.
E91 and entanglement-based QKD	Shared entangled signals and selected measurements generate key and test correlations. An entanglement-based implementation is not automatically device independent.
Decoy-State QKD	Vary source intensities to bound yields and errors of relevant photon-number components. Security depends on the source model, randomization, and finite-statistical bounds.
Measurement-Device-Independent QKD	Two characterized senders transmit states to an untrusted joint-measurement station. Removes the need to trust the measurement station under the protocol model; source assumptions remain.
Device-Independent QKD	Bell correlations constrain an adversary with minimal internal device characterization. Still needs specified isolation, setting choices, authentication, adversary model, and finite-size analysis.
Quantum Randomness	Generate raw data, certify conditional entropy, and extract nearly uniform bits. Randomness is relative to side information; a noisy-looking histogram alone is insufficient.
Blind Delegated Quantum Computation	A limited client delegates a computation while hiding protected information. Blindness protects privacy; verifiability is a separate guarantee against incorrect output.

Shor and Preskill give an idealized BB84 security proof connecting key generation with entanglement purification. It should not be transplanted unchanged to arbitrary sources, detectors, or finite datasets. Broadbent, Fitzsimons, and Kashefi give a delegation construction with a client capable of preparing selected single-qubit states; it must not be described as a generic single-server protocol with a purely classical client. Pironio and collaborators demonstrate the role of Bell correlations in certified randomness.

A no-signaling check

In qubit teleportation, Bob’s conditional states before correction are $X^bZ^a\rho Z^aX^b$, with each outcome pair $(a,b)$ occurring with probability $1/4$. Without the classical record, his state is

$$\begin{aligned} \rho_B&=\frac14\sum_{a,b=0}^1X^bZ^a\rho Z^aX^b\\ &=\frac I2. \end{aligned}$$

It carries no dependence on the unknown input. The classical message enables recovery; pre-shared entanglement does not provide faster-than-light communication. No-Cloning and No-Signaling explains the broader constraints.

Compare complete protocols

For any claimed rate, state the denominator: attempted transmissions, accepted rounds, elapsed time, or consumed entangled pairs. Report both success probability and conditional quality for a heralded protocol. A secure key rate is obtained only after error correction, privacy amplification, finite-size penalties, and authentication accounting; raw detection or coincidence rate is a different quantity. For a network, additionally identify which nodes must be trusted and whether stored states survive the waiting times.

References

• Azuma, Koji, Kiyoshi Tamaki, and Hoi-Kwong Lo, “All-photonic quantum repeaters,” Nature Communications 6, 6787 (2015), arXiv:1309.7207 — repeater architecture without long-lived matter memories.
• Broadbent, Anne, Joseph Fitzsimons, and Elham Kashefi, “Universal blind quantum computation,” Proceedings of FOCS 2009, 517–526 (2009), arXiv:0807.4154 — delegated computation with a limited quantum client.
• Nielsen, Michael A., and Isaac L. Chuang, Quantum Computation and Quantum Information, 10th anniversary edition, Cambridge University Press, 2010, doi:10.1017/CBO9780511976667 — ideal communication protocols and resource accounting.
• Pironio, Stefano, et al., “Random numbers certified by Bell’s theorem,” Nature 464, 1021–1024 (2010), arXiv:0911.3427 — device-independent randomness certification.
• Shor, Peter W., and John Preskill, “Simple proof of security of the BB84 quantum key distribution protocol,” Physical Review Letters 85, 441–444 (2000), arXiv:quant-ph/0003004 — security under the stated BB84 model.