Photonic assembly

A quantum communication system comprising a quantum state encoder a quantum state decoder,

• wherein the quantum state encoder comprises a first photonic assembly comprising
• a first section, the first section comprising a first substrate;
• and
• a second section , the second section comprising a second substrate;
• wherein the first photonic assembly comprises a first interferometer, the first interferometer comprising a first plurality of passive photonic elements and a first phase modulator;
• wherein the first phase modulator is provided on the second section;
• and
• wherein the first plurality of passive photonic elements are provided on the first section,
• wherein the first interferometer comprises a first optical path and a second optical path;
• wherein the first plurality of passive elements comprises a first coupler, a second coupler, and a first delay line;
• wherein the first coupler couples an input of the first interferometer to the input of the first optical path and to the input of the second optical path,
• wherein the second coupler couples the output of the first optical path and the output of the second optical path;
• and
• wherein the first delay line is provided the first optical path or is provided in the second optical path,
• wherein the first phase modulator is provided at an output of the second coupler;
• and wherein the quantum state decoder comprises a second photonic assembly comprising:
• a third section, the third section comprising a third substrate;
• and
• a fourth section , the fourth section comprising a fourth substrate;
• wherein the second photonic assembly comprises a second interferometer, the second interferometer comprising a second plurality of passive photonic elements and a second phase modulator;
• wherein the second phase modulator is provided on the fourth section;
• and
• wherein the second plurality of passive photonic elements are provided on the third section,
• wherein the second interferometer comprises a third optical path and a fourth optical path;
• wherein the second plurality of passive elements comprises a third coupler, a fourth coupler, and a second delay line;
• wherein the third coupler couples an input of the second interferometer to the input of the third optical path and to the input of the fourth optical path,
• wherein the fourth coupler couples the output of the third optical path and the output of the fourth optical path;
• and
• wherein the second delay line is provided the third optical path or is provided in the fourth optical path,
• wherein the second phase modulator is provided at an input of the third coupler.