Quantum computer and quantum memory

A quantum memory comprising:

• a crystal doped with a Pr3+ ion and formed of Pr3+:
• YCl3, a Y3+ and a Cl− having nuclear spins of smallest magnetic moments among ions having a valence of +3 and ions having a valence of −1, respectively, the crystal being configured to store quantum information indicating a photon that couples with a transition between one hyperfine level of 3H4(1) levels of the Pr3+ ion and one hyperfine level of 3F3(1) levels of the Pr3+ ion;
• and
• a light source configured to supply a laser beam resonating with a 3H4(1)-3F3(1) transition of the Pr3+ ion,
• a host crystal included in the crystal satisfying three conditions recited below:
• a first condition that maximum phonon energy of the host crystal is not more than 350 cm−1 to satisfy the condition that a homogenous broadening of a 3F3(1) level of the Pr3+ ion resulting from relaxation due to phonon emission is smaller than respective hyperfine splits of a 3H4(1) level and the 3F3(1) level of the Pr3+ ion;
• a second condition that a site of the Pr3+ ion does not have inversion symmetry, and the Pr3+ ion has a Stark level in which the 3H4(1) level and the 3F3(1) level of the Pr3+ ion are not degenerate;
• and
• a third condition that each atom (ion) in the host crystal has no electronic magnetic moment.

A quantum computer comprising:

• a crystal doped with a Pr3+ ion and formed of Pr3+:LuCl3, a Lu3+ and a Cl− having nuclear spins of second smallest magnetic moments among ions having a valence of +3 and ions having a valence of −1, respectively;
• an optical resonator containing the crystal and having a resonator mode that couples to a transition between one hyperfine level of 3H4(1) levels of the Pr3+ ion in the crystal and one hyperfine level of 3F3(1) levels of the Pr3+ ion;
• and
• a light source configured to supply a laser beam resonating with a 3H4(1)-3F3(1) transition of the Pr3+ ion,
• a host crystal included in the crystal satisfying three conditions recited below:
• a first condition that maximum phonon energy of the host crystal is not more than 350 cm−1 to satisfy the condition that a homogenous broadening of a 3F3(1) level of the Pr3+ ion resulting from relaxation due to phonon emission is smaller than respective hyperfine splits of a 3H4(1) level and the 3F3(1) level of the Pr3+ ion;
• a second condition that a site of the Pr3+ ion does not have inversion symmetry, and the Pr3+ ion has a Stark level in which the 3H4(1) level and the 3F3(1) level of the Pr3+ ion are not degenerate;
• and
• a third condition that each atom in the host crystal has no electronic magnetic moment.

A quantum memory comprising:

• a crystal doped with a Pr3+ ion and formed of Pr3+:LuCl3, a Lu3+ and a Cl− having nuclear spins of second smallest magnetic moments among ions having a valence of +3 and ions having a valence of −1, respectively, the crystal being configured to store quantum information indicating a photon that couples with a transition between one hyperfine level of 3H4(1) levels of the Pr3+ ion and one hyperfine level of 3F3(1) levels of the Pr3+ ion;
• and
• a light source configured to supply a laser beam resonating with a 3H4(1)-3F3(1) transition of the Pr3+ ion,
• a host crystal included in the crystal satisfying three conditions recited below:
• a first condition that maximum phonon energy of the host crystal is not more than 350 cm−1 to satisfy the condition that a homogenous broadening of a 3F3(1) level of the Pr3+ ion resulting from relaxation due to phonon emission is smaller than respective hyperfine splits of a 3H4(1) level and the 3F3(1) level of the Pr3+ ion;
• a second condition that a site of the Pr3+ ion does not have inversion symmetry, and the Pr3+ ion has a Stark level in which the 3H4(1) level and the 3F3(1) level of the Pr3+ ion are not degenerate;
• and
• a third condition that each atom (ion) in the host crystal has no electronic magnetic moment.