  We construct an entangled quantum heat engine (EQHE) based on two two-spin
systems with Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction.
By applying the explanations of heat transferred and work performed at the
quantum level in Kieu's work [PRL, 93, 140403 (2004)], the basic thermodynamic
quantities, i.e., heat transferred, net work done in a cycle and efficiency of
EQHE are investigated in terms of DM interaction and concurrence. The validity
of the second law of thermodynamics is confirmed in the entangled system. It is
found that there is a same efficiency for both antiferromagnetic and
ferromagnetic cases, and the efficiency can be controlled in two manners: 1.
only by spin-spin interaction J and DM interaction D; 2. only by the
temperature T and concurrence C. In order to obtain a positive net work, we
need not entangle all qubits in two two-spin systems and we only require the
entanglement between qubits in a two-spin system not be zero. As the ratio of
entanglement between qubits in two two-spin systems increases, the efficiency
will approach infinitely the classical Carnot one. An interesting phenomenon is
an abrupt transition of the efficiency when the entanglements between qubits in
two two-spin systems are equal.
