Quantum Technologies in the 21 century

Eugene DemlerHarvard University

Quantum Physics

Atoms MoleculesNuclei Materials

Fundamentalquestions

Importantapplications

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Moore‘s law

From Gordon Moore “No exponential if forever”

faster = smaller

Every 18 months computer power doubles

Suppress quantum

Our alternatives:Exploit quantum

H = E

“Quantum Technology is a radical departure in technology, more fundamentally different from current technology than the digital computer is from the abacus”.

William D. Phillips,1997 Physics Nobel Laureate

“When we get to the very, very small world – say circuits of seven atoms - we have a lot of new things that would happen that represent completely new opportunities for design. Atoms on a small scale behave like nothing on a large scale, for they satisfy the laws of quantum mechanics…”

“There's Plenty of Room at the Bottom”(1959)

Richard Feynman

Quantum Computers

Exponential speed up of number factoring Shor (1994)

Quadratic speed up in database search Grover (1996)

Highlights

Bits and QubitsA quantum bit (qubit) is the quantum mechanical generalization of a classical bit, a two-level system such as a spin, thepolarization of a photon, or ring currents in a superconductor.

0, 1

Classical bit

Physical realization via a charged/uncharged capacitor

0 V

1 V

Q QQuantum objects are waves and can be

in states of superpositionQubit

spin ring-currentphoton

polarization

Classical & quantum gatesThe combination of the classicalgates allows us to construct all manipulations on classical bits.

Is there a set of universal quantum gates ?How does such a set look like ?

Manipulation of a quantum bit is much richer than of a classical bit. We can perform rotations around the x -, y -, and z - axis

Two-qubit gate gate:XOR (CNOT)

Includes entangling gates

Quantum registers

= a0 [000] + a1[001] + a2 [010] + a3 [011] a4 [100] + a5[101] + a6 [110] + a7 [111]

Parallel quantum information processing

Quantum computing = smart computing

Example: need to find the tallest wooden block

Traditional computing: measure every block and compare them.

Smart computing: bring blocks together and check which of them stands out.Requires new types ofoperations!

Example: Deutsch’s algorithm (1985)We are given a 1-bit function f(x): one bit in, one bit out.

→ Is f(x) constant or balanced?

x f(x)0 01 0

x f(x)0 11 0

x f(x)0 11 1

x f(x)0 01 1

f(x) = 0 f(x) = xf(x) = xf(x) = 1

constant balanced

classically, require 2 queries to determinewhether f(x) is constant or balanced

Quantum computers use “massive quantum parallelism” to speed up computations

[0] + [1] x → x y → yf(x)[0] [1]

[0][0]

[0][1]

+[1][0]

[1][1]

[0][f(0)f(0)]

+[1][f(1)f(1)]

single (quantum) query

NOT measure

[01][0] if f(x) constant

[01][01] if f(x) balanced

NOT[0][0] if f(x) constant

[1][01] if f(x) balanced

Quantum computing = smart computing

Quantum Factoring P. Shor (1994)

Second example

15 = 3 5 38647884621009387621432325631 = ? ?

Quantum Factoring

A quantum computer can factor numbers exponentially faster than classical computers

Look for a joint property of all 2N inputse.g.: the periodicity of a function

f(x) = sin(2x/p) p = period

P. Shor (1994)

f(x) = ax (Mod N) r = period (a = constant)

s

O s

2

G s

0x

Whose phone number is 458-0223 ?

Grover’s search algorithmUnsorted database search

Grover algorithm sees all entries at once,marks the right answer and amplifies it.Geometrical interpretation: state vector rotates towards the answer every iteration

Number of steps O(N1/2) vs O(N)

Quantum Hardware

Candidate QubitsA cross-disciplinary race

NMR

ions

Quantumdots

Photons in opticalcavities Atoms in cavities

Superconductingcharge and flux based

Trapped Atomic Ions

Yb+ crystal

~5 m

8 qubitsRecord holders in the numbers of q-bitsand complexity of operations8-qbits in 2006

Science 2009

Nature 2009

Elements of a successful quantum computer

Existence of coherent qubit systemIsolation from environment for sufficient time

Universal set of gates. Reproduce all operations

InitializationBegin calculations from well defined initial state

ReadoutAbility to access and read qubits

ScalabilityNecessary to increase the number of bits without fundamental change in strategy

Your name

Other QC designs:

Nitrogen + Vacancyimpurity in diamond

Fluorescence of an array of single impurities in diamond

Most recent QC designs: NV Centers in Diamond Room temperature quantum computing M. Lukin (Harvard)

Other QC designs:Most recent QC designs: Topological QCA. Kitaev (2003) Landau Institute/Caltech

=5/2 state is a quantum topological statewhich allows topological quantum computations

Microsoft Q Station is fully devoted to topological QC Cost: about 20 million in the last 5 years

Quantum Technologies beyond quantum computing

Quantum computers with thousands of bits,which can be used to factorize large numbersare still several years away.

Already now quantum technology has important applications

World’s most precise clocks

The new aluminum clock would neither gain nor lose one second in about 3.7 billion years

It employs the logical processing used for atoms storing data in experimental quantum computing

Compact versions of super-precise atomic clocks can be the basis for navigational systems of the future. They may eliminate the need for human drivers

NIST’s “quantum logic clock” based on Al ionsis world’s most precise clock

Accuracy of GPS is determined by the precision of clocks. Current accuracy of the order of meters.Needed centimeters.

Quantum sensing and imaging

Nitrogen vacancy colorCenter in diamond combined with quantum information processing can be used for ultrahigh resolutionmagnetometry

Potential applications forreal-time, non-invasive imagingin medecine

Quantum Communications

Needed for the world soccer Cup in Russia in 2018?

Critical communication link in the 2010 World Soccer Cup used quantum technology

Solving fundamental problems with quantum technologyOpen challenges in physical sciences

Understand and design quantum materialsone of the biggest challenges in Physics in the 21 century

High temperature superconductivity (electricity)

Magnetism (data storage)

10-20% of electric power is lost in transmission. This problem can be solved by creating lossless transmission lines from high temperature superconductors

Why we can not solve these problems with conventional computers

Example: Electrons on a lattice. SSystem underlying many solid state and materials problems.Magnets, High Temperature Superconductors, Spintronics, …

Each doubling allows for one more spin ½ only

Modeling: from airplanes to wind-tunnels

Quantum simulations: understanding high Tc superconductors using artificial quantum systems

Concluding remarks

International Centers for Quantum Sciences and Technology

Harvard-MIT CenterFor Ultracold Atoms,Boston USA

Institute for Quantum Optics andQuantum Information of the Austrian Academy of Sciences,Innsbruck, Austria

The Institute for Photonic SciencesBarcelona, Spain

Max Planck Institute of Quantum OpticsMunchen, Germany

Needed: Quantum Center in RussiaInternational, interdisciplinary Center of excellence focused on exploring a new area of quantum science & technologyKey component: a new model of research institute based in Russian Federation (RF)Goals: obtain fundamental understanding of complex quantum systems & their control, train new generation of scientists & engineers, develop quantum processing technologies, including•Ultra-fast information processors•Absolutely secure communication systems•High precision navigational and time-keeping systems•All-optical energy efficient communication/processing • Novel quantum materials with properties designed on demand• Novel energy harvesting technologies • Ultra-sensitive quantum biomedical diagnostic technologies

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The first solid-state transistor(Bardeen, Brattain & Shockley, 1947)The first solid state transistorBardeen, Brattain & Shockley, 1947

Albert Einstein (1879-1955) Erwin Schrödinger (1887-1961)Werner Heisenberg (1901-1976)

Quantum Mechanics: A 20th century revolution in physics

Quantum objects are waves and can be in states of superposition.

CAT CAT

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…BAD NEWS!decoherence

Decoherence: A peculiarly quantum form of noise that has no classical analog. Decoherence destroys quantum superpositions and is the most important and ubiquitous form of noise in quantum computers

2. Rule #1 holds as long as you don’t look!

[1][0]

[0] & [1]

or

1. Quantum objects are waves and can be in states of superposition.

“qubit”: [0] & [1]

1. Individual atoms and photonsion trapsatoms in optical latticescavity-QED

2. SuperconductorsCooper-pair boxes (charge qubits)rf-SQUIDS (flux qubits)

3. Semiconductorsquantum dots

4. Other condensed-matterelectrons floating on liquid heliumsingle phosphorus atoms in silicon

scales

works

Quantum Computer Physical Implementations

1981. First idea: Feynman q. simulator

1995. Shor’s algorithm; Cirac-Zoller gate

2000. Diverse approaches

2002. 2-qubit gates

2006. Quantum byte (trapped ions)

2008. Error correction threshold reached

Start of q. comp

(Trapped ions, neutral atoms, cavity QED, semiconductor, superconducting, linear optics,impurity spins, single molecular cluster, NMR,...)

2015 (?). Few qubit quantum processorsQ. simulators

timeline forquantum computationtimeline forquantum computation

Current status• Small-scale (<100 km) quantum networks

realized, early commercialization efforts• Challenges: speed, distances

Albert Chang (Duke Univ.)

Other QC designs: Single electron quantum dots

Albert Einstein (1879-1955) Erwin Schrödinger (1887-1961)Werner Heisenberg (1901-1976)

Quantum Mechanics: A 20th century revolution in physics

Quantum objects are waves and can be in states of superposition.

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Quantum Key Distribution via photon qubits through air or optical fibers

45

Nuclear magnetic resonanceFirst realization of Quantum Computer: NMR

1. Individual atoms and photonsion trapsatoms in optical latticescavity-QED

2. SuperconductorsCooper-pair boxes (charge qubits)rf-SQUIDS (flux qubits)

3. Semiconductorsquantum dots

4. Other condensed-matterelectrons floating on liquid heliumsingle phosphorus atoms in silicon

scales

works

Quantum Computer Physical Implementations

Quantum communications• Quantum teleportation for information transmission Small-scale (<100 km) quantum networks realized

• Memory elements connected by quantum channels• Quantum conversion between light and matter