Method for determining a quantum communication setup, quantum communication setup, computer program, and data processing system

1 . A method for determining a quantum communication setup, the method being carried out in a data processing system and comprising:

providing a component set indicative of a quantum communication setup comprising quantum communication components of at least one of a first communication device, a second communication device, and an eavesdropping device;

selecting an action of a set of actions each indicative of a further quantum communication component and each selectable with a selection probability depending on the component set and a reward value;

adding the selected further quantum communication component to the component set, thus generating an updated component set;

determining, from the updated component set, a quantum model comprising a quantum state of at least one of the first communication device, the second communication device, and the eavesdropping device;

determining, from the updated component set and the quantum model, a maximum key rate by optimizing over an optimization parameter set comprising quantum communication component parameters;

adjusting the reward value depending on the size of the maximum key rate in relation to a previous maximum key rate; and

iteratively repeating the above steps until a termination criterion is satisfied, yielding an optimal component set and an optimal setup parameter set.

2 . The method according to claim 1 , wherein the quantum communication components comprise optical components, the optical components including at least one of beam splitters and phase shifters.

3 . The method according to claim 1 , wherein selecting the action is carried out by a reinforcement learning agent.

4 . The method according to claim 3 , wherein the reinforcement learning agent is a projective simulation agent.

5 . The method according to claim 1 , wherein the selection probability for selecting one of the set of actions corresponds to a reinforcement learning policy and depends on an exponential of a weight depending on the component set and the action.

6 . The method according to claim 1 , further comprising removing identical quantum communication components from the updated component set.

7 . The method according to claim 1 , wherein the quantum state comprises a plurality of optical modes, and wherein a random number comprising randomly generated informational bits is encoded using optical modes.

8 . The method according to claim 1 , wherein the quantum model further comprises quantum measurements carried out in at least one of the first communication device and the second communication device.

9 . The method according to claim 1 , further comprising:

determining, from the quantum model, a postselection set comprising measurement outcomes accepted by the first communication device and the second communication device,

wherein the postselection set is determined by determining, for each measurement outcome, first information about a corresponding informational bit provided to the second communication device and leaked information about the corresponding informational bit provided to the eavesdropping device.

10 . The method according to claim 1 , wherein the maximum key rate is determined via a global optimization method that includes a simulated annealing.

11 . The method according to claim 1 , wherein the optimization parameter set comprises at least one of an intensity value, a phase shift value, and a postselection mask bit, and wherein the optimal setup parameter set comprises at least one of an optimal intensity value and an optimal phase shift value.

12 . The method according to claim 1 , further comprising: before adjusting the reward value, if the maximum key rate is less than or equal to the previous maximum key rate, iteratively including another further quantum communication component in the updated component set, updating the quantum model, the postselection set, and the maximum key rate until a maximum number of iterations is reached or the maximum key rate is greater than the previous maximum key rate.

13 . The method according to claim 1 , further comprising outside the data processing system:

preparing the quantum communication setup according to the optimal component set and the optimal setup parameter set.

14 . A computer-readable, non-transitory storage medium storing instructions that, when executed by a processor of a data processing system, causes the processor to execute a method of designing a quantum communication system, the method comprising:

providing a component set indicative of a quantum communication setup comprising the quantum communication components of at least one of a first communication device, a second communication device, and an eavesdropping device;

selecting an action of a set of actions each indicative of a further quantum communication component and each selectable with a selection probability depending on the component set and a reward value;

adding the selected further quantum communication component to the component set, thus generating an updated component set;

determining, from the updated component set, a quantum model comprising a quantum state of at least one of the first communication device, the second communication device, and the eavesdropping device;

determining, from the updated component set and the quantum model, a maximum key rate by optimizing over an optimization parameter set comprising quantum communication component parameters;

adjusting the reward value depending on the size of the maximum key rate in relation to a previous maximum key rate; and

iteratively repeating the above steps until a termination criterion is satisfied, yielding an optimal component set and an optimal setup parameter set.

15 . A data processing system configured to determine a quantum communication setup, the data processing system comprising:

a hardware processor configured to perform steps including:

providing a component set indicative of a quantum communication setup comprising quantum communication components of at least one of a first communication device, a second communication device, and an eavesdropping device;

selecting an action of a set of actions each indicative of a further quantum communication component and each selectable with a selection probability depending on the component set and a reward value;

adding the selected further quantum communication component in the component set, thus generating an updated component set;

determining, from the updated component set, a quantum model comprising a quantum state of at least one of the first communication device, the second communication device, and the eavesdropping device;

determining, from the updated component set and the quantum model, a maximum key rate by optimizing over an optimization parameter set comprising quantum communication component parameters;

adjusting the reward value depending on the size of the maximum key rate in relation to a previous maximum key rate; and

iteratively repeating above steps until a termination criterion is satisfied, yielding an optimal component set and an optimal setup parameter set.