# US 2014/0197831 A1 · Absorbtion-Based Detection Of Spin Impurities In Solid-State Spin Systems

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- Number: US 2014/0197831 A1
- Document ID: US20140197831A1
- Status: Published application
- Kind: A1
- Application number: 14/125,072
- Filed: 2012-06-12
- Published: 2014-07-17
- Earliest claimed: 2011-06-13
- Assignees: President and Fellows of Harvard College
- Inventors: Ronald Walsworth
- Web page: https://patentgrep.com/patent/US20140197831A1

## CPC

- G01R 33/323: {Detection of MR without the use of RF or microwaves, e.g. force-detected MR, thermally detected MR, MR detection via electrical conductivity, optically detected MR}
- G01R 33/1284: {Spin resolved measurements; Influencing spins during measurements, e.g. in spintronics devices}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

Absorption based detection of spin states of spin impurities within a solid-state spin system, such as NV centers in diamond, is implemented by measuring the absorption intensity of an optical signal applied to the spin impurities, i.e. change in intensity of the optical signal after the signal has been transmitted through the solid-state spin system. During optical excitation of the spin impurities, microwave pulses are applied to the sample at a frequency tuned to the ESR frequency. The relative populations of the spin states of the impurities, which provides information regarding variables of interest such as an external magnetic field or a quantum information protocol, is determined from the ratio of the absorption intensity of the optical signal when the microwave pulses are turned on, to the absorption intensity of the optical signal when the microwave pulses turned off.

## Claims

### Claim 1

A method comprising:
determining electronic spin states of electronic spin impurities within a solid-state spin system, by measuring an absorption intensity of an optical signal applied to the spin impurities.

### Claim 2 (depends on 1)

The method of claim 1, wherein measuring the absorption intensity comprises measuring a change in intensity of the optical signal after the signal has been transmitted through the solid-state spin system, due to absorption of at least some of the photons in the optical signal by the spin impurities.

### Claim 3 (depends on 1)

The method of claim 1, wherein the spin impurities are NV (Nitrogen-vacancy) centers, and wherein the solid-state spin system is a diamond lattice.

### Claim 4 (depends on 1)

The method of claim 1, wherein the act of determining the electronic spin states comprises determining the relative populations of different spin states of the spin impurities; and
further comprising using the relative spin populations to obtain information about a variable of interest.

### Claim 5 (depends on 4)

The method of claim 4, wherein the variable of interest comprises one of
an external magnetic field;
an external electric field; and
a quantum information protocol.

### Claim 6 (depends on 4)

The method of claim 4, wherein the NV center has:
a spin triplet ground state that is further split by spin-spin interactions into an ms=0 ground state and ms=±1 ground states, separated from each other by an energy split of about 2.87 GHz;
an ms=0 excited state and ms=±1 excited states; and
a metastable spin singlet state.

### Claim 7 (depends on 6)

The method of claim 6, wherein the optical signal applied to the spin impurities has a frequency and a strength sufficient to cause optical transitions into the metastable single state from the mms=±1 excited states, and to cause subsequent decay from the metastable state primarily to the ms=0 ground state, so as to cause substantial depletion of the ms=±1 excited states over time, and to cause the ms=0 ground state to become dominantly populated over time.

### Claim 8 (depends on 4)

The method of claim 4,
wherein the solid-state spin system comprises a bulk diamond sample containing NV centers, and wherein the act of measuring the absorption intensity comprises the acts of
applying the optical signal to the sample at a frequency that is tuned to optically excite at least some of the spin impurities in the sample;
during the optical excitation, applying to the sample one or more microwave pulses that are resonant with electronic spin transitions; and
detecting output optical radiation after the optical signal has passed through the bulk diamond sample, so as to determine the absorption intensity as measured the by change in intensity of the optical signal due to absorption by the spin impurities.

### Claim 9 (depends on 8)

The method of claim 8, wherein a time evolution of the spin states of the NV centers is mathematically describable as a function of optical transition rates between the spin states and the Rabi frequency, by a mathematical formula given by:

ρ
i

t
=
A
ij

ρ
j
,
where ρi is the population in the ith state and Aij is the transition rate from the jth state to the ith state.

### Claim 10 (depends on 9)

The method of claim 9,
wherein coherent mixing between the ms=0 ground state and the ms=±1 ground states is mathematically describable by optical Bloch equations.

### Claim 11 (depends on 9)

The method of claim 9, wherein the act of determining the absorption intensity comprises integrating the ground state populations over a detection time period.

### Claim 12 (depends on 10)

The method of claim 10, further comprising determining the relative populations of the electronic spin states from the ratio of the measured absorption intensity of the optical signal when the microwave pulses are turned on, to the measured absorption intensity of the optical signal when the microwave pulses turned off, using a mathematical formula given by:
A
on
A
off
=
ρ
11
on
+
ρ
22
on
ρ
11
off
+
ρ
22
off

|
equilibrium
.

### Claim 13

A system comprising:
an optical source configured to generate light that can optically excite electronic spin states of electronic spin impurities in a solid state lattice, when applied to a sample containing the spin impurities and the solid state lattice;
a microwave source configured to generate microwave pulses that can be applied to the sample during optical excitation by the light, at a frequency tuned to the electronic spin resonant frequency of the spin impurities; and
a detector configured to detect output optical radiation after the optical signal has passed through the sample, so that the absorption intensity of the optical radiation can be measured.

### Claim 14 (depends on 13)

The system of claim 13, wherein the detector is configured to determine the absorption intensity by detecting a change in intensity of the optical signal after the signal has been transmitted through the solid-state spin system, the change caused by the absorption of at least some of the photons in the optical signal by the spin impurities.

### Claim 15 (depends on 13)

The system of claim 13, further comprising the sample that includes the electronic spin impurities.

### Claim 16 (depends on 15)

The system of claim 15, wherein the sample comprises bulk diamond and wherein the electronic spin impurities comprise NV centers in the diamond.

### Claim 17 (depends on 13)

The system of claim 13, wherein the optical source is a laser that is tunable to a frequency of about 532 nm.

### Claim 18 (depends on 13)

The system of claim 13, further comprising a processing system configured to calculate the relative populations of the electronic spin states from the measured absorption intensity.

### Claim 19 (depends on 18)

The system of claim 18, wherein the processing system is further configured to calculate the relative populations of the electronic spin states of electronic spin impurities, using a mathematical model that relates the relative populations of the electronic spin states to the ratio of the absorption intensity of the optical signal when the microwave pulses are turned on, to the absorption intensity of the optical signal when the microwave pulses turned off, by a formula given by:
A
on
A
off
=
ρ
11
on
+
ρ
22
on
ρ
11
off
+
ρ
22
off

|
equilibrium
.

### Claim 20 (depends on 19)

The system of claim 19, wherein the processing system is further configured to provide an absorption intensity signal by integrating the ground state populations over a detection time period.