vacuum

◼ vacuum[] returns the vacuum vector in the occupation number (vc) representation for a basis that has been previously defined using makebasis.

◼ The occupation number representation in sneg is adapted to systems consisting of a finite number of lattice sites. The vacuum in this context is the state where no particles are present on any of the sites.

◼ See also: basis, makebasis, op2ndx, ndx2op, goodopQ, ap, vc, vc2ops.

Further examples

Load sneg and declare some quantities

<< sneg`sneg`;
snegfermionoperators[c, d];

Construct a basis for two lattice sites c and d

makebasis[{c[], d[]}]

The vacuum state is the state where no particles are present.

vac = vacuum[]
FullForm[%]

Single-particle states can be constructed by adding individual particles to the vacuum

ap[c[CR, UP], vac]
ap[c[CR, DO], vac]
ap[d[CR, UP], vac]
ap[d[CR, DO], vac]

Many-particle states are obtained by repeatedly adding single particles. The order is important, since we are dealing with fermions.

ap[c[CR, UP], ap[c[CR, DO], vac]]
ap[c[CR, DO], ap[c[CR, UP], vac]]
ap[c[CR, UP], ap[d[CR, DO], vac]]
ap[d[CR, DO], ap[c[CR, UP], vac]]