Quantum computation with two-electron spins in semi-conductor quantum dots

Tuukka Hiltunen

Research output: ThesisDoctoral ThesisCollection of Articles


A quantum computer would exploit the phenomena of quantum superposition and entanglement in its functioning and with them offer pathways to solving problems that are too hard or complex to even the best classical computers built today. The implementation of a large-scale working quantum computer could bring about a change in our society rivaling the one started by the digital computer. However, the field is still in its infancy and there are many theoretical and practical issues needing to be solved before large-scale quantum computing can become reality. In digital computers, data is stored in bits. The quantum equivalent is called a qubit (quantum bit) and it is basically a quantum mechanical two-level system that can be in a superposition of its two basis states. There are many different proposals for implementing qubits, but one of the most promising ones is to encode the qubit using electron spins trapped in semiconductor quantum dots. Singlet-triplet qubits are spin qubits where the two-electron spin eigenstates are used as the qubit's basis. The required one and two-qubit operations have already been demonstrated experimentally by several research groups around the world in this qubit architecture. The most severe factor limiting the implementation of larger systems of qubits is decoherence. The qubits are not isolated systems, they interact with their environment, which can lead to the loss of quantum information. Few-electron systems can be simulated accurately using first principle methods that become too taxing when the particle number increases. The topic of this thesis is the simulation of quantum dot singlet-triplet qubit systems using accurate exact diagonalization based methods. The emphasis is on the realistic description of qubit operations, both single-qubit ones and those involving the interaction between neighboring qubits. The decoherence effects are also discussed alongside with certain proposals to alleviate their effects.
Translated title of the contributionKvanttilaskenta käyttäen kahden elektronin spini-tiloja puolijohdekvanttipisteissä
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Nieminen, Risto, Supervising Professor
  • Harju, Ari, Thesis Advisor
Print ISBNs978-952-60-6199-3
Electronic ISBNs978-952-60-6200-6
Publication statusPublished - 2015
MoE publication typeG5 Doctoral dissertation (article)


  • quantum computer
  • spin qubit
  • singlet-triplet qubit
  • entanglement
  • decoherence
  • configuration interaction
  • Hubbard model


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