Quantum information technology

1. Quantum Information
Technology
MITCHELL WALLS

2. n = p × q
p and q Prime Number
Calculate p and q given
only n.
2048 bit number takes
10¹¹ years versus a under
a second for QC.
Is Quantum Computing (QC) Faster?

3. Qubit Dephasing by Landau-
Zener Interferometry
•Double Quantum Dot qubit with electron states (1,
0) → (1, 1) ↔ (2, 0) → (1, 0).
•S singlet state with 1 in electron in each quantum
dot or 2 in 1 and 0 in the other.
•Current of electron tunneling across dots show the
interference.
•ε(t) refers to Detuning energy levels resulting in
superposition. Called Avoidance zones in LZSM
Interferometry.
Forster, F., et al. "Characterization of qubit dephasing by Landau-Zener-Stückelberg-Majorana interferometry." Physical review letters 112.11 (2014): 116803.

4. What makes a good qubit
A qubit needs to be isolated from the environment to prevent errors
(decoherence).
The lower the temperature the more accurate and less error that is
introduced to the system.
For a two electron Gallium Arsenide double quantum bit qubit lower
temperatures result in higher coherence times. Solid line is electron-
phonon coupling, dashed is computed numerically for double
quantum dots Hamiltonian.
Forster, F., et al. "Characterization of qubit dephasing by Landau-Zener-Stückelberg-Majorana interferometry." Physical review letters 112.11 (2014): 116803.
Coherence times vs Temperature given the detuning
energy

5. Quantum Error Correction
•Preventing errors in qubits requires implementing error correction.
•A single logical qubit can be encoded across multiple physical qubits. The larger number of
qubits the lower the probability of error.
Zeng, B., et al. "Encoding a logical qubit into physical qubits." Physical Review A 71.2 (2005): 022309.

6. Lossy
Channel
Devitt, Simon J., William J. Munro, and Kae Nemoto. "Quantum error correction for beginners." Reports on Progress in Physics 76.7
(2013): 076001.

7. Error correction on other
Quantum Gates
The Toffoli gate is one way to check the
decoded quantum information for errors
after a previous gate.
This gate is defined as a controlled-
controlled-not gate. It is a universal
reversible logic gate. Any reversible gate
can be constructed from Toffoli gates.
Cory, David G., et al. "Experimental quantum error correction." Physical Review Letters 81.10 (1998):
2152.

8. Toffoli Gate Error
Correction

9. Fidelity of
Trichloroethylene
(TCE)
Graph of the fidelity of TCE after
decoding and subsequent Toffoli
gate.
Helps filter out fluctuations in the
local magnetic field.
Where the Fidelity is the probability
that one quantum state will identify
as another.
Using error correction the slope of
the fidelity decreases drastically.
Cory, David G., et al. "Experimental quantum error correction." Physical Review Letters 81.10 (1998):
2152.

10. Bandwidth Issues
with Error
Correction Code
•Bandwidth becomes a concern when
dealing with software-based error-
correction.
•99.999% of the instructions in the
instruction stream of a typical
quantum workload stem from error
correction.
•Hardware error-correction like the
controlled not gates will be required
as quantum computers become larger
with more qubits.
Tannu, Swamit S., et al. "Taming the instruction bandwidth of quantum computers via hardware-managed error
correction." 2017 50th Annual IEEE/ACM International Symposium on Microarchitecture (MICRO). IEEE, 2017.

11. Steger, M., et al. "Quantum information storage for over 180 s using donor spins in a 28Si “semiconductor vacuum”." Science 336.6086 (2012): 1280-1283.
Quantum Information Storage for over
180 s Using Donor Spins
 99.995% 28Si and contains 5 × 10¹¹ cm⁻³ of 31P and 5 × 10¹³
cm⁻³ of the acceptor boron, making it p-type semiconductor
 Uses hyperfine coupling D₀ electron spin of the phosphorous
atom.
 This induces nuclear spin using valence electrons.
 Storage and retrieval information by entanglement of electron
and nuclear spins for qubits.
 Manipulating the hyperfine electron coupling energy levels
using hyperpolarizeration
 Finally the readout is done by Auger-electron-detected
magnetic resonance.

12. Long Term Quantum Storage
•Nuclear spins seem to be the most promising for solid state storage of qubits.
Steger, M., et al. "Quantum information storage for over 180 s using donor spins in a 28Si “semiconductor vacuum”." Science 336.6086 (2012): 1280-1283.