Quantum computers, quantum computations

Take-home message

The quest for a quantum computer reminds me of the

Motivation

Microprocessor 80486dx2

Electronic lamp

Meters

Nanometers

Moore’s law

40 years

Outline

History
Principles of quantum computation
Di Vincenzo criteria
Superconducting qubit
Some algorithms
Architecture
Challenges and problems

History in facts

1982 – R. Feynman predicts possibility of quantum computations

1935

2012 – S. Haroche & D. J. Wineland winn Nobel prize

History in diagrams

Classical vs quantum: speed up

What is beyond?

Down to small size = forward to quantum physics

Quantum Mechanics: Quantum Information

What is all about or new applications of quantum physics

“Hacking” crypto
Keeping

What is QC?

QC is the physical device that utilizes quantum properties

Classical ≠ Quantum

Hardware

Software

Boolean logic

Quantum logic

Classical

Quantum

(Principle of
excluded middle)

(Superposition & hidden symmetry)

Algorithm complexity

Easy

Hard

Input

Classic C

Quantum C

Hard

Qubit = Quantum bit

Bit

Qubit

Entangled states (EPR)

Interference – Schrödinger's Cat

Quantum parallelelism

Parallel quantum algorithm

Universal gate set

Operation
Gates:
NOT
Hadamar
XOR

Principles of quantum computation

Computation: unitary evolution

Readout: measurement

Avoiding decoherence

Di Vincenzo criteria

Selectivity (addressing each qubit)
High sensitivity = Good control
Large decoherence

Quantum computer by Cirac & Zoller (1995)

Ions in trap

Qubit: micro or macro?

Measurement duration:
Limitations:
Energy splitting:
Qubit = 1 electron

Superconductors: macroatoms

Qubit: charge or phase
Control: magnetic flux
Readout: SQUID, SET
T=10 mK
1 qubit

Superconducting qubit: overcoming decoherence

Shnyrkov et al, 2007
τdecoh→ s, T → 1

Flux qubit: theory

… & experiment

qubit

gate

V-I SQUID (V.Shnyrkov, G. Tsoi, 1990)

quantum

classic

ScS-контакт, m= 26, C= 8 pF, βL= 3,83

Quantum coherence

Single-qubit gate

Experimental results for the charge-phase qubit placed in the region of

2-qubit gate (DiVincenzo et al, IBM qubit)

Find the period: Shor’s algorithm

Hidden symmetry

ay=0 - amplification; ay=1 - depression

Classic algorithm : 2n =N
Quantum algorithm: 2n/2 = √N
Unsorted database
Merlin

Database search

Grover’ algorithm

Input
Flip (Merlin)
Mirroring

Grover’ algorithm: experiment

4-level system

QIR=Quantum Intermediate Representation
QASM=Quantum Assembly Language
QPOL=Quantum Physical Operations Language
QCC=Quantum Computer Compiler

Architecture

Quantum computer: challenges

Decoherence (state instability)
Scaling (few number of qubits)
Input-output control
Extreme

Quantum abyss

# кубитов

~5

<100

# операций

Есть

Надо

>1000

>109

Шум ↓

Технологии ↑

Алгоритмы ↑

Ошибки ↓

?

When, Where, Who & hoW?

2 qb — 1999, 7 qb —

Alumni

Vadym Kliuchnikov
Post doc researcher @ Microsoft Research
http://research.microsoft.com/en-us/people/vadym/

Sergii Strelchuk
Junior Research Fellow