Where is the modern QKD heading?

Where are modern quantum key distribution technologies heading? The article discusses one of the new protocols for quantum key distribution based on random groupings and measurements of Bell states. Using his example, it is proposed to think about the future of quantum cryptography.

If the words qubit and Bell states horrify you, then I recommend looking under the spoiler and reading a brief theoretical background. If you are familiar with the terms of quantum informatics, then you can go directly to the protocol (although it will not be superfluous to refresh your knowledge).

Theoretical introduction

What is a qubit?

Consider some two-level quantum system, examples of which can be a fermion with spin s = 0.5 or the state of polarization of an electromagnetic field (photon). Formally, such a system is described by the Hilbert space of two quantum states . In accordance with the principle of superposition, the most general normalized state in this Hilbert space can be represented as:

(.: qubit, quantum bit). , , . , , 0 1.

. a b 4 . , , . . 2 . , :

, .

, . — , , . , — . , , φ⁺, :

, , 00 11 . , , 0 1, .

, , , — . , 0, 1, , . - , . , 0, , 00 — , 0. , , .

, , . , , — , . — , . , .

. (.: Quantum Key Distribution, QKD) — , . , , , , , .

. QKD 1984 . BB84 . QKD, E91, --.

QKD (.: Bell States Measurement, BSM). 2008, . QKD, , . , . .

, , , . . Protocol*.

, . () , , (). . , , , .

, 1 4. , 1 2, 3 4 . 1 3, 2 4 . φ^- φ⁺, :

, , , . , . , , . .

• 1. . , , . P . ( , ). , .

  
  
  
  
  

• 2. . .

  
  
  
  
  

• 3. . . .

  
  
  
  
  

• 4. . P. , True 5 1 . , False, 1 .

  
  
  
  
  

• 5. . c 1 4 , R ( ). R_A R_B . R_A C_A, . C_B R_B.

  
  
  
  
  

• 6. . C_B D_B D_B . D_A D_B. , 7; , 1 .

  
  
  
  
  

• 7. . R'_A R'_B, . , R'_A = R'_B, R'_A — R_A C_A, R'_B.

  
  
  
  
  

, . , QKD .

QKD . . , (BB84, E91).

QKD () . , — . p_d = 1 - 10^-9, :

, , .

QKD . - 2007 140 BB84. , - . , 2017 .

: ID Quantique, MagiQ Technologies Inc. . 2004 . 2013 QKD, ID Quantique, . 2019 .

.

QKD

, , . QKD.

• QKD , . , , .

  
  
  
  
  

• , . , QKD .

  
  
  
  
  

• 2008 , " , ". QKD , .

  
  
  
  
  

There will be no unequivocal conclusions here, I suggest leaving the open final. At the moment, both in science and industry, two main groups have formed: for and against "quanta". Which group do you belong to? Do you think there is a future for quantum cryptography and QKD in particular?

PS I would be glad to have an open discussion, comments and suggestions.